Although I'm certainly not a fan of John McCain, in the interests of fairness, I do think I should point out that his head-to-head polling numbers vs. Obama and in particular, against Hillary, are really good.

From SurveyUSA (Which should have polled Fred Thompson's numbers as well, but didn't),

First of all, from Missouri, a state Bush carried by 7 points in 2004,

Giuliani 43%
Clinton 47%

Giuliani 44%
Obama 47%

Romney 42%
Clinton 49%

Romney 43%
Obama 48%

Huckabee 47%
Clinton 45%

Huckabee 51%
Obama 41%

McCain 50%
Clinton 44%

McCain 51%
Obama 41%

Next up is Washington, a state Kerry won by 7 points in 2004,

Giuliani 38%
Clinton 51%

Giuliani 35%
Obama 57%

Romney 38%
Clinton 54%

Romney 32%
Obama 63%

Huckabee 40%
Clinton 54%

Huckabee 35%
Obama 60%

McCain 49%
Clinton 46%

McCain 43%
Obama 52%

Next is Oregon, a state Kerry won by 4 points in 2004,

Giuliani 39%
Clinton 52%

Giuliani 35%
Obama 56%

Romney 34%
Clinton 57%

Romney 32%
Obama 63%

Huckabee 38%
Clinton 55%

Huckabee 35%
Obama 60%

McCain 49%
Clinton 45%

McCain 47%
Obama 47%

I admit that I am not a fan of John McCain and also that numbers can change a lot over the course of the campaign, but I do have to at least say that at the moment, McCain looks to be several orders of magnitude stronger than the other Republican candidates.