Best Affiliate Networks
Online Affiliate marketing is where you introduce traffic to an online retailer by getting visitors to your site to clickthrough to the retailer's site to purchase goods or services. Every time one of the people you introduce to the online retailer makes a purchase, they pay you commission or an introduction fee.
The real benefit of affiliate marketing to the internet marketer is that they don't need to own or ship goods, nor do you have to handle payments - you just need to have a website or landing page that they can use to redirect traffic to the retailer. From the retailer's point of view, they get customers they wouldn't ordinarily have got, and these customers are the best sort - qualified customers who are interested in the product and are at the end of the buying cycle.
Success in affiliate marketing depends on two things - having a good landing page and signing up with the right affiliate networks.
Most online merchants won't actually deal with you directly - they will deal with you through an affiliate network. The benefit of using an independent third party is that the network tracks all the clicks, sales and transactions, providing independent verification to both the merchant and to the affiliate marketer, and handles all the payments.
This page lists the best affiliate programmes based on my personal experience with them, and as I'm a UK marketer, the page is biased towards sharing knowledge about British merchants and affiliate networks.
Affiliate Window
Affiliate Window is a UK affiliate network which lists pretty much all the major UK online merchants from Marks and Spencers and Sainsburys to Oddbins the wine mechants and Dixons the electrical goods retailer, as well as a host of smaller merchants.
If you are looking to sell branded goods, Affiliate Window is ideal as they will give you access to these brands.
They are very picky about who they accept as an affiliate - and as a gesture of good-will they ask you to pay a £5 deposit to them when you apply to join, which is refunded as soon as you reach your first £25 in commission. Note that when you apply to them, if they decline you, you forfeit your £5 - so make sure that your landing page is already set up, has pagerank and is getting decent traffic before you apply, to improve your chances of being approved. The landing page might take a good three months to set up and gain pagerank, but it's worth the wait to avoid disappointment (you can always monetize with Amazon while you are waiting for your site to mature).
I had set up my landing page on Squidoo, as Squidoo is pretty flexible about affiliate marketing - in particular their text modules accommodate banners (use the "text with big picture" module). I nursed my page and built backlinks and traffic to it, and only applied to Affiliate Window when I had a pagerank 3. I was accepted, and then placed the banners on my lens.
Results: good. As long as you've built the site properly and targeted the right keywords and placed your banner above the fold, you should get clicks through and sales.
Affiliate window merchants usually offer a 30 day cookie (some have longer cookies), and pay between 5% and 15% in commission (about 10%-12% is the norm).
Their tracking statistics are brilliant - when you get a sale, they show you when the person clicked through and when the transaction occurred. This was a real eye-opener for me and gave me a real insight into online customer behaviour. It turns out that very few people will buy immediately when they click through. Instead they browse around, perhaps bookmark the page. go away to look at other prices and then come back another day to make the purchase. I've had people come back to purchase a full 23 days after they clicked through. I've also had people click through, go away to think about it, come back to make a purchase and then come back again a few days later to purchase some more - and as it was in the 30 day cookie period, I got credited for all sales. It has brought home to me that 30 day cookies are important.
One word of warning: Not all merchants who say they have a 30 day cookie actually have a thirty day cookie - they often employ "last click tracking" which means that your cookie can last only a couple of minutes. See this thread on the Affiliates4u forum about the John Lewis affiliate scam where someone lost all their Christmas sales due to this. So before you sign up check the fine print and it might be worth emailing the merchant to check they don't employ "last click tracking".
Once a transaction has occurred, it takes 7 days further to validate it (so it goes from pending to confirmed) and then Affiliate Window invoice the merchant. Once they receive the money, it goes into your account to be paid out on the next payday. Affiliate Window pay twice a month on the 1st and on the 15th, by bank transfer, once you have at least £25 in your account. They aggregate payments for all their merchants - so if you are affiliated to several merchants, with several small sales, they will simply add them together and pay you once you've got £25.
I'm happy with the tracking, have been paid on time by them.
Amazon
Registering as an affiliate with Amazon.com (or Amazon.co.uk or any of the other local Amazons) is easy. You simply click on the "Amazon Associates" tab and apply to join and verify your email - you need to specify a website, but they aren't picky about inspecting them. So of course this is the first port of call for those who want to try affiliate marketing.
However, this ease comes with drawbacks. Amazon commissions are low (usually 5% rising to 7.5% and capped at £25 for electrical goods). Even worse they have a 24-hour cookie. This means that in order to for you to profit from referring traffic to them, your visitor needs to purchase almost straight away. If they are the type who likes to browse and come back, you won't get paid. When I had Amazon on my Squidoo hubs, I got lots of clicks through to Amazon, but such trivial sales that it will take aeons to make payout. Once I changed the affiliate to Affiliate Window (see above) sales really picked up.
My conclusion: Amazon works well if you are selling something which people have an imperative need to buy immediately. For any goods they can wait a few days to buy (such as books, DVDs etc), you are better off with an affiliate that offers a longer cookie. There is one caveat to this - because Amazon is a trusted brand, people happily click the ads, and you get a lot of unexpected sales if you put the link on high traffic pages - see this eye-opening video post about Amazon, which explains why.
Amazon pay two months in arrears, either by bank transfer when you reach $25 or by cheque when you reach $100.
I am a member of both Amazon UK and Amazon USA - I joined Amazon UK first, and when I applied to join Amazon USA, they seemed to link my associates accounts as they automatically created the US account with the same password as the UK account. However, they keep the payments separate (as they are in different currecies).
Finally, one caution about Amazon (learned the hard way). Don't promote Kindle ebooks - Amazon pays you ZERO for it even if the ebook sells for the same as the paperback. Ebooks are becoming more popular with readers, as they can download the backlists of their favourite authors - but if you are selling mainstream published fiction/non-fiction and want to put the ebook on your page, you are better off seeking to become an affiliate of the publisher directly (some mainstream publishers are listed in the Affiliate Window and Commission Junction networks).
Commission Junction
Commission Junction is an American affiliate network that has a vast number of online merchants on it's books, including most of the brandnames. They are also signing up merchants from across the globe - I've seen brand names from the UK and Germany on there, so even if you are not American it might be worth signing up as they probably have an affiliate program for one of your domestic online retailers (they also cater for non-English advertising).
I first came upon them when I was looking at a merchant's site and decided I'd like to be an affiliate - the merchant had a link to Commission Junction who handled their affliates for them, and I clicked through and signed up. It turns out that that retailer had automatic approval. Other merchants on the Commission Junction platform usually approve people manually, and will turn you down if you are too new or if your sites aren't mature enough.
Therefore before signing up for merchants, make sure that your landing page or blog is more than three months old, has backlinks and traffic and has some pagerank. Many affiliate marketers tend to apply too early for the merchant programs because they are chomping at the bit to make money - but that usually results in a decline from the merchant, so it's worth waiting and taking your time to do it right. Remember that until you have traffic, you won't make any money anyway, so the traffic building must come first.
Sometimes whether they approve or deny depends on your geographic location. For instance, the UK retailer Argos (which has a similar product range to Amazon) does it's affiliate marketing through CJ, and approves all UK affiliates automatically. US affiliates will have difficulties, as Argos only sells within the UK and you would have to prove you get a lot of UK traffic.
When you join, you need to list the sites you will be putting ads on (go to the account tab and then website settings). When you then select the ad for the particular merchant, you need to specify which site you are putting it on (this will generate a code in the affiliate link). They also require the publisher to have activity on their account (page impressions of ads, clicks etc) - if you have no activity for six months your account is closed.
They provide detailed tracking (though not quite as good as Affiliate Window's), allowing you to see which ads/banners are performing and which are not, and which sites the sales have come from. They track the performance of the publishers, calculating their average CTR over the last 7 days and the last 3 months and also the level of sales for these periods. This is something to keep an eye on as some merchants will only accept you if your existing performance is at a certain level.
Commission Junction aggregates payments from all their merchants and will either pay by cheque when you reach $100 or by direct deposit when you reach $25 (direct deposit is only available for the USA, Canada and some western european countries).
Affiliate Forums
I'm a British affiliate marketer, and I tend to use the Affiliates4U forum as my first port of call when I have a question.
They have sub-forums for all the afiliate networks that British affiliate marketers use - eg Affiliate Window, CJ UK, Linkshare UK, PaidonResults, etc etc. More importantly, the affiliate managers of the major UK online retailers (Marks and Spencers, Argos, Sainsburys, Dorothy Perkins etc) hang out there and will give you an answer straight away to any question/problem you have. They tend to post about their latest promotions there too, so it's well worth looking in on the forum to see what is going on.