Typepad seems popular. Wordpress is the option many choose, I'm even converting my "static" sites to it, because the plug-in development is amazing. With anything else, there's a smaller pool of developers working on that aspect.
I'm not worried about using it, I'm just wondering what other types are out there for a new site I'm working on. Keep them coming, some that hasn't already been mentioned.(FREE forgot to mention free)
I forgot what kind of software PerezHilton.com uses but I believe you have to pay for it. It must be pretty good considering most blogging software is free.
Not sure what you're after, but here's a list of Open Source CMSes: http://opensourcecms.com/ It appears to me that site is using Wordpress. If you look in the html, there is a reference to wp-content at the top for the style sheets. Seems like a dead giveaway to me.