WordPress seems to be using DTCoreText in their iOS app, which is a library for natively rendering HTML in text views (w/o UIWebView). The developer also has a great iOS blog.  The closest thing I could find for Android is HtmlSpanner.

Anyone have ideas for other projects or technologies to check out?  Maybe we should talk to people at WordPress, as it seems their problem space is somewhat similar to ours (many installs, user-created content, custom styling, multiple platforms ...).

Regards,

Brian