Amazon - I took a ton of pressure off of EPN in 2010 and it paid off greatly. Good targeted sites will convert that one day cookie. Great plugins like the PHPZon Wordpress plugin make it easier than ever to earn with the Amazon affiliate program.
Google Adsense - I doubled my 2009 Google Adsense income in 2010. What more can I say? I am very happy with the program and have a good understanding of what sites it works best on. I could live of that income alone.
Ebay Partner Network - Although no longer my top earner by choice by taking the pressure off of it and diverting it to other programs, I learned how to best maximize the EPN QCP model to my liking. It remains a solid way to earn money, especially using the PHPBay plugin by Wade. Program has earned me a ton of money over the years. Still love it.
Share-A-Sale - This affiliate company does not get enough recognition, but represents some great companies that convert fantastically. If you have not signed up and looked around at what they offer, you really should.
Commission Junction - I have been with these guys for a long time. I have a few companies that I represented for years that do very, very well for me. No complaints.
Clickbank - Great company to sell ebooks on. Easy to manage. I do a ton with this blog and another MMO blog that I run with them as well. Never had a problem with them.
Google Affiliate Network - They get more and more new companies every week it seems like. I have a few favorites with them.
Pepperjam - They have had their struggles, but I have a few sites that do well with a few of the companies they affiliate manage.
Linkshare - Same as Pepperjam really. What I do point their way, does convert.
Neverblue - Just really scratching the surface with these guys, but got several checks in 2010 from them. I want to try to use more of their stuff in 2011.
These are really just my major ones above and I use another handful of companies as well. Webmaster Magazine has a great article in the January 2011 issue of the top 50 advertising and affiliate networks for 2011. Worth a glance.