I've got 3 competitons! Mabye few more on my head as I post.
1.) Skin Competiton - Prize 1 Year FreeHost
2.) Referal Competiton
3.) Post a Thon
Thats the three I have, on my forum on the Referal Competiton I got 245 new members, and Post I got 5671 more post so it seems liek a good idea.