A couple friends of mine got great results (more than they could handle) with Google’s program. I think it’s called Ad Words or something like that. It does cost you though. I think yahoo has something similar.

You can also try to join groups that might be interested in your site, and without spamming the group you can let it be known that you have a related site. For example, if you have a site dedicated to video games, visit the many video game forums and get the word out. But again I must emphasize, don’t spam people. Don’t just drop a message on them and never return. Become a part of the group, participate, become known.

Enter award sites, and join directorys! It also depends on what kind of site it is.