Atrios is on Air America right now.
Although I'm more than pleased at his success, he's about the most public secret pseudonymous commentator I've yet ran across.
(Were I invited onto Air America- which is probably unlikely given my current posting frequency- I'd at least use a voice disguiser. Mostly because they sound cool, sure, but pseudonymity requires some sacrifices.)
Edit: it's been pretty good, although I think that Janeane and Sam's take on Bush's backers misses the historical context of the Republican spin machine: to attempt to manufacture their own counterparts to FDR, Wilson, LBJ (to an extent), and other notable Democrats. The record of Republican presidents since the start of the century hasn't been exactly inspiring, and the ones from the last 30 years are almost hilariously bad. They've got to cover for that.
(Yes, that includes Reagan. The only reason Reagan's foreign policy wasn't a total failure was Mikhail Gorbachev.)
The spin is because now that there's a war on, they really, really want Bush II to be the new FDR. They'll do and say anything to do that. They're also desperate to keep Clinton's reputation in the toilet, because his relatively successful presidency and sexual dalliances are a serious threat to the core tenet of social conservatism: that private (sexual) morality determines success.