Last night, I tried out 2 Pocket PC blogging tools: Diarist and PocketBlogger.
Diarist supports several popular blogging engines, including Blogger, CommunityServer, and LiveJournal. The only quirk I've noticed so far is that the title field doesn't map to the titles in my blog posts for some reasons - rather it shows up as heading level 2 text at the top of the posts.
Update: Kevin blogs that this is a limitation of the Blogger API, and in his next version he's considering switching to the ATOM API to address the problem.
PocketBlogger looks a little nicer in and "finished" in terms of UI. It only works with Blogger accounts, though. It has the added advantage of being able to query your blog for previous posts so you can delete or edit them.
Niether tool currently supports offline blogging or photo uploads. Both would be "nice to have" features, in my opinion.
Both are free, but their authors are more than happy to accept donations to support future development.