There are many different advertisers that you can allow on your site, even in parallel. They differ in the relevance of the ads to your posts which is important because you usually get paid in clicks (CPM, clicks per million) not by the impressions of the ad. Usually AdSense displays very relevant ads.
However, Google pays only once you reach $100. Especially for beginners, this is an incentive to use an advertiser that pays earlier. Other may start paying at a lower limit, such as bidvertiser, which starts at $10, or adbrite, which offers an adjustable minimum. You can usually choose between payment by checks and paypal. AdSense also transfers money on bank accounts.
Adbrite rates your site by visits and unique visits. It offers the option of defining an alternative ad program, such as AdSense, which will be shown if a minimum ad price (in CPM) is not reached. AdBrite also allows selling space for text links by days, weeks, and months. Note that Adbrite's charges a 30% commission, so you should add 30% to your other ads CPM (multiply by roughly 1.42).
Both AdBrite and Bidvertiser offer a referral program, which means that you gain a little money if people sign up from a link at your site and once they start making money. I put the links below (if you consider signing up with them it would be nice, if you do from here).
|Monetize your Website or Blog with BidVertiser|
Another possibility for advertising is an affiliate program. The main difference is that you earn either from leads or from sales (EPC - earn per click). There are many networks you can join and choose ads by sales region and category. Google just started its Adsense Affiliate Network. Some affiliates provide product feeds, while others only provide static links which you have to customize manually.
I show one example for an affiliate program below. Abebooks lets you search books, first and second hand, among thousands of book stores. They pay 5% commission on sales generated from your referrals.
Very important to increase the click-rate is the placement of your ads. To know exactly the effectiveness of your ads at different locations, AdSense offers you so-called channels to look at the statistics. You can create channels together with ads on-line at AdSense. Google analytics offers observing AdSense statistics, so you can have everything in one place.
Note that, although ads with images may have more appeal, they can make your site load very slowly. As we all know, too many ads drive visitors away.