Google Adwords
Google Adwords allows you to design your ads and select how much money you want to spend on your campaigns.
Kontera
Kontera helps you get your ads on relevant sites and relevant posts on blogs! They use a keyword system to display your ads!
Bidvertiser
Bidvertiser also allows you to choose how much money you will pay per click and choose some details about your ad and where you want it to be displayed!
Adbrite
Adbrite for advertisers is much like anyother one. You pick target keywords, channels, and categories for your ad to be displayed on! You can also manage the sites your ad displays on.
Affiliations
Now this is not exactly advertising in the sense that you don't spend money. It is more of free advertising! You get free placement and exposure by affiliating with other websites that have similar user base as yours. This can help increase traffic and popularity of your site!
