Who should I drop, and why?

Well, definitely you should drop one of your batters. All your pitchers are top-notch. I would drop Marcus Giles if anybody. The rest of your players are either performing extremely well, or are reputable batters who should kick up their game a bit as the season progresses. Marcus Giles is a great all-around player, but at 2B, Kelly Johnson gets you everything. Even though you sacrifice a bit in SB and average, HR and RBI's are higher for Johnson.