I have used the dreaded fanny pack in the past. I also have the Donner bag mentioned earlier in the thread - which I love on days when I find I have to carry just a little more (rain poncho as a good example). In general, we're of the "try not to carry anything at all" camp when it comes to the parks.
That said, I've recently purchased this bag (in black) from QVC that I'm anxious to try out on our trip next week. It's smaller than the Donner bag but just big enough for my camera and has interior slots for cards and park tickets. I used it on a trip to the state fair last week and it worked out great!
Travelon Nylon Expandable Crossbody Bag