Luke is once again the player who signed the most over the course of the season. I'm pretty much at the point where I try to let other fans get his autograph since I've got his signature so many times. He always seems like a nice guy and talks to the fans while he's signing. I listed Luke in this category last season too, but he really deserves his own category.
The following three relief pitchers signed almost every Sunday during the season (Sunday's are the day pitchers can warm up on the field since there's no batting practice).
Albers has been inconsistent on the mound over his time in Baltimore, but he's typically been a good signer at least.
Ohman was sent to the Marlins at the trade deadline, but he signed very frequently before being sent to Miami. I think he signed every card I had of him before the trade, so I was fine with it.
I've heard that some other people had trouble getting Cesar's autograph this year, but not me. He was always the first player to come back to the dugout after B.P. and would normally sign early on. Cesar really upped his signing game this season; I listed him in the kinda-good category last year.