MoveOn.org, though not a registered non-profit, is now able to offer their private contributors tax-deductible benefits when they make their donation through the San Francisco Foundation Community Initiative Fund (a non-profit, 501(c)3 organization). Other organizations providing financial support include the Iraq Peace fund ($20,000 grant - an effort of the "Tides Foundation", tidesfoundation.org), and a grant of $100,000 in 2002 from the Richard & Rhoda Goldman Fund. Coincidentally, the Goldman Fund also provided the now irrelevant Million Mom March with a $4.3 million grant in 1999. Looks like they may be operating some front organizations. They may keep their books legit.
Pacifica Radio is a 501c3 that definitely violates the political activism clause of their (Pacifica's) status. I haven't been able to get anyone excited about that violation (there are a handful of other posters who also comment on it but most people dismiss it).