About a year ago Google offered new referral program for Adsense - Firefox with Google Toolbar. If you referred people to download and install a fresh copy of Firefox with Google Toolbar, you would get 1$. There were also scripts like “Internet Explorer killer” that was showing banners to clients with Internet Explorer encouraging them to use Firefox. I`ve earned some bucks with this referral program, but lately I`ve noticed, that earnings have decreased pretty much.

Should I say more? Ok, it`s in beta but it already has at least 7.5million (content from partner library) books. Most I guess are just a preview with links where to buy, but still the preview is nicely done!
Visit: Google Books Search