I signed up with Adbrite and am sporting Adbrite ads on blogs and my 5 sites.
First go to Adbrite and sign up. You can create Ad Zones. I created a leaderboard ( 720* 90), Custom and Skyscraper ( 160*600 ). They will give you the ad code and you can insert it in your blog templates. Along with Adsense ads, you can insert Adbrite ads. Blogger gives you the option to inserts ads anywhere on the blog. I am getting regular checks from Adbrite.
The Adbrite leaderboard is nice and takes only 720*90 space. You can insert it in between blog posts. If you blog daily and if you post, say, five times, you get five blog pages containing these ads and all these will add to your revenue !
You can go to www.google.com/adsense and sign up. You can get the ad code and you can insert in your blog and web pages.
The best is the large rectangle. Next is the medium rectangle and the Skyscraper. The leaderboard is OK. Use of fonts and colors to match the color or your blog or site pays rich dividends. I am getting regular checks from Google !
Good luck with Adbrite and Adsense ads !