Someone had put together a pretty neat blog software comparison chart that allows you to compare functions of the different blog engines easily.
Also, a list of blogging software tools is available from Yahoo’s directory that is worth looking at. I’m firmly in the WordPress camp, but I’ve heard good things about MoveableType, and Drupal as well. I don’t believe in paying for blogging software, so find it very hard to understand why people use Type Pad/Moveable Type, Expression Engine, or Radio Userland. I just can’t see what they offer as being any better than what I get for free.