Westhost has good, cheap packages, as little as $3.95 a month paid two years paid in advance, $4.95 if paid yearly. They have phpBB (a good, full-featured BB system) and a bunch of other standard applications you can install and uninstall through a web-based interface. You also get a virtual server, so you can create and delete user and email accounts at your leisure.
I've used them for a very long time, and recommend them. I won't even tell you who I am to get the referral credit, just suggesting on merits.