Matt read my mind; I was thinking the same thing before even reading the posts.
I would have the alternator checked out. Also, who ever checks it make sure your car is warmed up, turn everything on to really work the alternator. Then check it right away, while it is still hot. The reasoning is the alternator diodes get weak when hot. Another area to check is all the battery connections, make sure there solid. Especially the fender ground, it was marginal from the factory and gets worse over time because the fender well has a drain right above it.
Also, I would like to vote for Diehard as a good replacement battery.
Good luck.
