I personally, used a Shared Host ( one of those 10 dollar for the whole year coupon deals ) when i started my forum, but once we hit around 20-30 users online at all times, the shared hosting went downhill bad. I would get all kinds of crazy Mysql Errors that had me searching the code tryin to figure out why when it turnd out it was just the server was overloaded. I since switched to Knownhost VPS but they offer a execellent Reseller plan to.
You Can get there Reseller Plan for as Low as 5 bucks a month and there VPS as low as 20 a month
What really shines with these guys thou is there execellent Tech Support. They always answer my questions within afew hours and even at 3am a real person actually answers the questions lol.
They have helped me recompile apache afew times due to various problems I had when i was setting up 2 apaches so i could run a SVN server but here's a link to there plans and there very reasonable IMHO.
Knownhost