Two math bloggers who write very entertaining posts (but have no RSS feeds alas) are John Baez and Doron Zeilberger.
Baez writes the well known column 'This Week's Finds in Mathematical Physics', which he cleverly called 'This week's..' instead of 'the week's...' so he didn't have to post something every week :). He discusses very technical material in mathematical physics, and is up to week 216 now (as of today), and his writing provides excellent model for a longer form exposition of technical content for the non-expert, something I hope theory CS folk can pick up on.
Doron Zeilberger's articles are less about mathematics and more about the process of doing mathematics, but are hilarious. He doesn't post that often, but all his articles are great to read. His most recent column is May 5, 2005.
This is all part of the theory advocacy process. We have to communicate the value of what we do to funding agencies, but we should try to communicate to a general audience as well. At the very least, the latter sharpens our skills for the former, and at best, we increase the awarenesss of the general population about the work we do.