Chuck Todd at The National Journal ranks the top five contenders for Presidential candidate from each party every month. Heading the list are John McCain and Hillary Clinton, no surpise there.
The rest of the Dems in the top five are; Mark Warner, John Edwards, Evan Bayh and Bill Richardson. The top tier R's are; George Allen, Mitt Romney, Mike Huckabee, and (sit down, everyone) Newt Gingrich.
Net fave, Russ Feingold is ranked in the pack with Bill Frist, Wesley Clark and Tom Vilsack. Interestingly enough, Rudy Giuliani doesn't show on the list except as a Wild Card. That list of Maybe-Never's includes Condeleeza Rice and John Kerry along with Al Gore and Michael Bloomberg.