There's a Wikipedia page that has a list of Celebrity Bloggers. Mostly it's bloggers who have some level of celebrity (Wonkette for example) and one or two actual Celebs.
Jamie Oliver has a decent site that is part diary and he seems to update it fairly regularly. Plus there's a quite a few recipes. The interface for the recipes is a little odd, though. It shows the last three and that seems it, but if you make a selection from the drop down box just above them, you get loads more.
The Shat has a web diary that it looks like he updates about once a month. Plus you can leave comments. That's right you can have dialogue (or at least pretend to, he doesn't seem too active in the comments, to be honest) with Bill Flippin' Shatner. Good times.
Wil Wheaton also has a blog with comments and he updates it regularly. He's been at it quite a while and is often very witty and quite aware of his place in the Star Trek universe. He also seem to have a regular spot talking about vintage video games over that the Onion AV Club. Cooler than you'd think.
ETA: Hannah points out in the comments that David Byrne's tour diary is rather good.