Based on the popular and not free Invision PowerBoard, Invisionfree is the free king of hosted forums. At the time of this writing there are 15 servers for their boards. You can change settings, create a new stylesheet, replace any image or button, assign moderators, ban people, delete posts, allow users to upload images, etc. Need I say more? I almost forgot, you can download thousands of skins and modifications. What’s the catch for this great service? Just a Google Adsense ad. I highly recommend Invisionfree, if you don’t want to set-up a board on your own server (or if you’re unable to). They’re currently working on their new custom forum system known as ZetaBoards, which will eventually replace the Invisionfree service (keeping all your posts and such).