Until recently there was a very good, reasonably low-priced service for submitting programs to the top 40 affiliate directories. Unfortunately, the owner moved on to something else and I'm not sure what's happened - whether the service has been taken over by someone else or not.
You can simply go to Google and search for "affiliate program directories". There's a whole heap of them come up and it will take you a while to work through them and to figure out which are the best to submit to. In most, if not all, cases it's free to get your site listed.
Now, I'm not sure if I'm allowed to do this or not and Wally or Allan will delete if it's inappropriate but you could begin by looking at the long list of directories here: