What is the best camera depends on a lot of things. How important are price, size/weight, image quality, speed, ease of use, flexibility, zoom range, etc?
In my opinion (as a Canon biased person), the overall best handheld digital camera on the market is the Canon 1DsM2. The only area where it is weak is in speed (fps, buffer size, buffer write speed). If you are shooting lots and lots of shots in a hurry or you want to save a little money, the Canon 1DM2n is also a great camera. You can pick up the 1DsM2 for just under $7,000 and the 1DM2n for only $3,600. Of course, at those prices, you don't get any lenses or memory cards.
I think Nikon also makes some similarly capable cameras, but I'm not very familiar with them.
These are where you'll get your best image quality without moving up to a camera designed more for shooting stricly on a tripod. If you don't want to spend that much or lug around a large, heavy, complicated camera with lots of lenses, you can also get some really nice DSLR and P&S cameras.