Andrew Sullivan has a nice analysis of the Republican and Democratic fields, focussing on how the winning candidates are largely defined by not being Bush:

And now we have the three potential Bush replacements: John McCain, the man who ran against him in 2000, voted against his tax cuts, excoriated his torture policy and assailed his Iraq occupation; Hillary, the wife of the man Bush succeeded and who beat his daddy; and Barack Obama, a young, charismatic JFK-liberal whose eloquence and erudition are almost textbook negatives of Bush’s folksy, faux-ignorant charm.

Interestingly, Sullivan is hot for Obama.  He likes the way Obama gets people fired up across party lines, and he thinks Hillary will be both too cautious and too divisive.