Each CPA network will have their own inventory of CPA offers, some exclusive only to that network.  You will also find many offers that are running in multiple networks.  It is a good idea to have accounts with them all so that you can compare and shop for the best payout rate.

Tip for applying:  When you apply for a publisher account, certain information is asked on the application.  Many will ask if you have a website.  If you do, great, go ahead and put your website in the application.  If not, you can just mention that you are a Pay-per-click advertiser (or you advertise in the search engines), and they should take you just like that.  Also, look out for their phone calls as they want to verify your application over the phone with you.  Don't get intimidated by them, they just want to make sure that you are a real person.

List Of CPA Networks

Incenticlick
Great selection of incentivizable offers -> this means that you can "bribe" your visitors in filling out offers.

Hydramedia
Huge selection of CPA offers.  If you can't find an offer in other networks, you will probably find something that works for you.

Azoogleads
Another network with great offer selections.

Clickbooth
Good selection of make-money-from-home type of offers