I use SMF. It has enough features for me, maybe not a lot mods though. It's free and you can get it installed on a free hosting or you can install it anywhere with Fantastico. It has a classic serious look and it is not so vurnelable for hacking, I guess.
Example.
Features.
I've came accross "vBulletin advanced" often lately. Anyone knows - is this an upgrade or a standalone edition? It looks like
this. The particular example forum is loading pretty slowly on my computer, I don't know is it a "heavy" script or is it a hosting...