With millions of installations worldwide, it is no wonder phpBB is one of the most popular ways to create and support a community. Been around since 2000. It has many plugins to choose from.
This is a very simple and nice looking board software that is easy to setup and maintain. It is faster, smaller and less graphically intensive as compared to other discussion boards.
MyBB is a powerful, efficient and free forum package developed in PHP and MySQL. It has a very nice layout and is easy to setup. Powerfull administration.