Wow! I was going to write my own too… but there are so many ready to use… and there are so badly written. I can’t use SMF or PhpBB because I always must take a look into code… The best which I found and finally using is MyBB.
@Shaun: How about adding some subcription functions to be notified when someone posts to a topic you posted to? This could be very handy as i’m normally not visiting this forums so often and sometimes forget that i asked some questions or something.