Google's been busy recently adding new Referral options to its Google AdSense program. Referrrals are affiliate links that instead of being PPC - Pay Per Click, you get paid for getting the user to do something like download a program. Now, instead of just buttons, you can have link referrals. These blend more easily with your site and can be integrated with your site content and styled however you like. However, AdSense still has a high level of control. You still have to place JavaScript ad code in the page and cannot change the text of the link.Also, there are some new referral programs. As well as the original AdSense, AdWords and Firefox, you now have Picasa and Google Packs. New ad colours have been added, but you need to choose US English to get them.However, I'm not sure that you do that well with referrals as the conversion is quite hard or underpaid.

Google Adsense - $100 when a user signs up and earns their own $100 in 180 days
Google AdWords - $20 when a user signs up and spends $100 in 90 days
Firefox - up to $1. Sometimes you can get only 10 cents for a Firefox referral as it depends on user location. US and UK are $1. Norway is $0.25. Other western nations about $0.50. Other countries like China and New Zealand are $0.10. Must be first time installation on Windows. Oh - it's not just firefox - it is FF with the Google Toolbar.
Picasa - photo editing software download for about $1. Must be first time installation on Windows


It's a good additional source of income but it won't earn you loads unless you are good at pushing the AdSense referral. I've been having a go with some of the new links and buttons and have seen a definite increse in CTR - Click Through Rate and conversion rates

Other affiliate networks are out there as well. I use Commission Junction which has the eBay.co.uk affiliate program (GBP 7 for a new user, GBP0.10 for a bid) and the eBay.com ($0.20 for winning bid). Also, there are a few other nice affiliate programs but I'm not too impressed. The Amazon.co.uk associates program is really good. I wrote one review for a product, put an Amazon link on it and had a sale almost instantly with about 7%. Just you don't want a small amount of money in loads of accounts because that way you'll never get paid!