I prefer InvisionFree, but I guess that's just force of habit.

There are advertising forums-- as in, forums whose main purpose is to advertise other forums. It might sound odd, but they do exist.
Spoiler Alert, click show to read: 

These are the two that I've used before, but there are quite a bit more if you're willing to do some digging. Personally, I found the sites a little too mercenary for my taste-- with posting packages, deals, etcetera, but it does give your fledgling forum a lot of exposure to potential members/people of similar interest.