Many people have started using Google's AdSense program, but there are some who find it a bit too uncertain or simply not suiting their own requirements from an ad program.
But thankfully for such people, there are many alternatives to AdSense which attempt to alleviate some of its shortcomings. Here is a list of the most noteworthy ones from the lot with a description concerning each one.
AllFeeds has a great pool of online advertisers to choose from. It also features many display formats that you can choose from. These include banners, buttons, XML feeds, DHTML pop-ups and so on. It also features real time reporting of your ad status. The site will mail a check every month, provided that you earn more then $25.00, while rolling over earnings for the next month if you don't. Another interesting thing about AllFeeds is that it integrates with Google AdSense, maximizing your earnings with AdSense.
MarketBanker allows you the unique possiblity to set the pricing for your site. It also allows you to allow or reject any link that appears on your site (although AdSense itself does a very good job of this as well, with URL filters) There's also a statistics section which will allow you to see how well your site is doing. The ads are small just like AdSense's and they're just as easy to set up. Also, registration for MarketBanker is free.
BidClix ( http://www.bidclix.com/PubTop.html)
BidClix is different because it has advertisers compete for clicks on your site, which in turn is meant to generate the highest possible profits for your page. It also has a very large pool of advertisers which ensure there are plenty of people to choose your site. However, it does require more polish on site contents then AdSense. As most sites, real time statistics are available and its very easy to get started with this service, but it's also very flexible.