•  Commission Junction -  www.cj.com  Perhaps best known for it’s CJU Santa Barbara seminar / networking bash, Commission Junction (aka CJ) is one of the larger affiliate networks. Their interface is easy to use, and their CJ performer status gives you an account manager and some other perks. Pays monthly but does have a minimum payout requirement. CJ’s advertiser side has a full assortment of managed and unmanaged programs that attract top and mid tier businesses and brands. 
• Linkshare -  www.linkshare.com Competing with CJ for the big fish spot is Link Share, who has it’s own yearly networking summit. They pay out every two weeks, and do not have a minimum requirement. Their interface is not as slick as CJ’s, and link tracking can get complicated. However, once again, this is a larger affiliate network with managed solutions for businesses, so it attracts larger and mid sized programs and brands. 
• Performics -  www.Performics.com In case you haven’t read the Google / DoubleClick merger notes closely enough, Performics is a property of DoubleClick. Their interface makes linkshare’s look like a walk in the park, and, while it also attracts larger businesses, just isn’t quite as polished as the two other guys. Payouts are monthly, though, so if it works for you, they’re still a reputable company. 
• Azoogle -  www.Azoogleads.com  Here’s the deal. Azoogle gives you your own affiliate manager to use as a sounding board, and you can choose from a list of programs. The interface is pretty easy, maybe as easy as CJ. A lot of the ads are promo based, and I noticed that some of the same advertisers  are running on either CJ or linkshare, so you may want to compare commissions and creatives.  
  
• ClickBank -  www.clickbank.com I’m not quite sure how to describe click bank, other than I love to hate them. In order to activate your account, you must have sales on 5 different credit cards with 5 different names and addresses, or they won’t pay your commissions. They’re mostly a small business software / online book network, but many affiliates swear by them. I’ll post more about the ins and outs of ClickBank.
• Share-a-Sale  www.Shareasale.com Until recently, I wouldn’t have listed this site at all, but I found one really cool product on there that changed my mind. You’ll find small to middle sized advertisers, so it’s great if you’re looking for unique products to promote. 

There are a lot of other Affiliate networks out there. Kowabunga! Technologies and NeverBlue ads are just two that I have bookmarked for future reference. TIP: Not all businesses go through affiliate networks, because these programs can charge flat fees or an additional percentage per action for management and recruitment fees.  Check your favorite websites to see if they run their own affiliate program.