Hot water heater leak?

I noticed that my hot water heater wasn't working yesterday when I tried turning on a hot tap and no hot water cam out. I went to the basement and saw that their was some water leakage (minor) from the unit. I checked the pilot light, and it was out. So, my 1st thought was that the pilot light went out and condensation was building due to cooling off. I re-lit the pilot light and it started up just fine. Got home tonight, however, and had the same issue. Took a good flashlight, looked into the access panel at the bottom and saw that their was water dripping onto the burner. I looked all over and saw that there was water on top of the unit. It looked like it was dripping from the vent that leads into my chimney. Does anybody have any ideas what's causing this? Do I have to buy a new heater? Thanks!