Whatever you end up with, avoid Toshiba drives; I've had two, and they both ran unacceptably hot. To the point where I had to keep the battery (mounted below the hard drive in this particular machine) out of the laptop to keep the drives within their allowable operating specs; given that the case on the Mac is aluminum it's likely that such a drive would make that part of the case unbearably warm to the touch.
As other people have said, Seagate and WD are good, and I've not had any issues with my Hitachi 7k60 either. Whatever brand you get, I recommend at least a 5400rpm drive; a 7200 would be even better and give you a noticeable performance boost over a 5400, at the possible expense of some nominal amount of battery life.