Maybe because of my earlier post about PPC and SEO, you might be thinking about using PPC.
One major PPC player is Google AdWords. But before you jump right in and create your adwords account, I highly suggest you check out this very important resource.
Adwords Demos and Guide at
It is a multi media tutorial about adwords. Your browser needs to support flash for this to work.
These are very helpful for beginners and a good resource to refresh yourself on adwords.
Other pay per click sites are Overture, Miva, Value Click.