Kontera - Kontera is not exactly the alternative of Google Adsense, but its something with works best with it. This is my second best choice after Adsense.
Adbrite - Adbrite is also a good Google Adsense alternative for making money online. This works best for website which has huge number of impressions. I use them for not-so-good type of websites which has quite high page impressions.
Amazon - I use amazon by putting just one or two related books/cd/dvds link on all my sites. It is just just put one related link of a book or related product and forget it.
TNX - A new and the best (in my opinion) link selling network which allows you to sell links on any sites (even PR0) sites (with or without traffic). So if you have a new site, you can make some money with TNX by just selling one unique link on a page.
WidgetBucks - If you have a website related to electronics products or other shopping related sites, then you can make good money with widget bucks. It doesn’t work well with other type of sites.
Adtoll - Adtoll is a new and promising adbrite type of advertising network, which allows you to sell your own links as well as RON links.
TextLinkAds - Another way of making money by selling links on your website. This is loosing more and more revenue day by day, but once upon a time, it was the best.