urldir has a pretty neat blog comparison tool called BlogComp. At this time you can use it to compare up to 5 of 27 different blogging tools. The list includes b2, Blogger, Movable Type, LiveJournal along with some other very popular ones. Note that it includes hosted services as well as host-your-own.
And while you’re there, take a look at the home page and archives. There’re some interesting links there, too, including a small article about TypePad, the Movable Type folks’ upcoming service based on the Movable Type engine.