Arguably the biggest affiliate marketer of them all is Amazon. You simply sign up, add the links to your site, and whenever someone clicks through and buys a product from Amazon you earn a commission. 

The most  popular book selling on this site at the moment, using Amazon, is American Accent Training. Having said that, I'm not actively promoting it. I put the link to the book on a page 3 years ago and it has sold over 100 copies since then.

I haven't done anything with it so it's continuous income with limited work. You can sign up with Amazon here.

A program that I've dabbled with is Ectaco's Electronic Dictionaries and Translators. I've made a number of sales but these items really require a proactive approach. If you've got a website where you can sell these strongly then you'll probably like the generous commission rates they offer. Click here then click on 'partnership' to find out more.

Google Adsense is another program I highly recommend. 

There are thousands of Associate and Affiliate programs online. I strongly recommend AssociatePrograms by Allan Gardyne. The man is a genius and his site is full of hundreds of pages of free content about how to make money from your website. 

I've been dealing with affiliate and associate programs since 1998 and I've finally decided to put together one myself, with the help of ClickBank. It's quite small at the moment as I only have one product to sell, but you can find out more about it here. Basically, if you have an ESL site you can sell my ebook - Become an English Language Conversation Tutor - and earn 33% commission. The affiliate page is here

The big secret about making money from websites is 'don't put all your eggs in one basket'. Unless you're a hugely successful site with thousands of unique visitors every month, it really isn't possible to make tonnes of money with just one affiliate program. The secret is to have multiple income streams and continually promote them across your website to people who actually want to buy them.

Alternately, if you're just wanting to get some money to pay your annual domain name charges and hosting costs, then a few links here and there that complement your site is usually enough, if your site has good content and can be found by search engines.

Hmm...search engine optimisation...now that's another story.