[LetYouDown]

I come up with 63: 44 flushes, 1 straight flush, 15 straights, 3 trip Jacks.

So if you're up against a random hand, the probability you have the best hand is:

1 - 63/C(45,2) = 93.6363...%

As Luzion noted, logic factors in here, but this should be right for one random hand.