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 (http://www.allfeeds.com/?action=publishers)
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 (http://www.marketbanker.com/mb/sell.php)
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.
Chitika (http://www.realcontext.com/index.php?option=RealContext:+Contextual+Targeting+Engine)
RealContext uses Artificial intelligence to retrieve the most relevant ads for your page. And there's an extra feature which makes RealContext unique as well. Keywords are selected based upon which previous selections payed off and which didn't. That means there's a constant feedback process that ensures you gain better revenue from your ads. It also supports blocking certain adds and child-safe filtering and many more options.
AdHearus (http://adhearus.com/webmaster.php)
AdHearus is a very feature-packed contextual ad provider. As with AdSense, advertisements are targeted but it doesn't stop here at all. The ads are very flexible, you can select from text-ads, banners, rectangles, pop-ups, pop-unders or skyscrapers. You can also display your own ads, through rotation, both on your site and on other affiliate sites, which makes AdHearus a hybrid with conventional advertising technologies. There's a very comprehensive on-line real time reporting feature and, as usual with such services, starting out is free and it's a breeze.
AffiliateSensor (http://www.affiliatesensor.com/)
AffiliateSensor has highly customizable ad blocks, which you can make for yourself with an easy to use on-line interface. You also get realtime reporting with clicks-by-domain, page and refferer. There's integration with Google AdSense as well, through the google_alternate_ad_url so AffiliateSensor can be used as a substitute for Google PSA's (Public Service Ads).
Kanoodle Bright Ads (http://www.kanoodle.com/about/brightads.cool)
Kanoodle's offering allows publishers to get ads related to topics or segments, and not the traditional keyword oriented ads. The site also groups publisher sites with advertisers by hand to ensure high-revenue generating ads. And speaking of revenue, the amount of money you receive is a clear 50% share of the amount of money Kanoodle recieves for an advertiser.
TargetPoint (http://publisher.targetpoint.com)
TargetPoint is oriented more towards content publishers. It offers full control over the look the ads, statistics over your site's overall performance and better revenue. It's free to register and you earn a guaranteed 60% of the total revenue. You can get payed with Paypal of Bank checks and (most times) wire transfers as well.
Clicksor (http://www.clicksor.com)
Clicksor will earn you as much as 60% from the amount of money your website produces. What you get is about the same as AdSense, there are targeted text ads, you can view the revenues from your website in real time. You can receive money via PayPal or through a check every two weeks, provided that you have earned more then $50. If you haven't made that much, your earning roll over to the next period.