Giuliani is way ahead of other Republicans in a new Quinnipiac poll, but Hillary still beats him by 3 points. The three point spread is negligable, and the poll shows Giuliani to be the most competitive against a Democratic ticket:

Republicans:
Giuliani 28 (-1 vs. June 13 poll)
Romney 15 (+5)
Thompson 12 (-3)
McCain 11 (-4)
Gingrich 7 (+2)

In the RCP National Average, Giuliani leads Thompson by 10.3 points.

Democrats:
Clinton 36 (+1 vs. June 13 poll)
Obama 21 (n/c)
Gore 15 (-3)
Edwards 9 (n/c)
Richardson 3 (+1)

In the RCP National Average, Clinton leads Obama by 18.7 points.

Head-to-Head:
Giuliani 43 - Clinton 46
Giuliani 42 - Obama 42
Giuliani 42 - Edwards 43

Thompson 38 - Clinton 49
Thompson 35 - Obama 46
Thompson 32 - Edwards 49

McCain 41 - Clinton 47
McCain 39 - Obama 43
McCain 37 - Edwards 45

As for Fred Thompson, because of his delay in getting in, his eventual entrance had better be more than stellar if he hopes to make up lost ground, the cause being a Republican base that has Giuliani and Romney on their mind, and not Thompson.