I'll raise you, I've picked up games multiple times on a given format AND on multiple formats.
Saints Row 2 (Twice on the 360, once on PC)
Mass Effect (PC x2, 360)
Mass Effect 2 (PC, 360)
Fallout 3 (PC x2, 360)
Fallout New Vegas (PC, 360)
Bioshock (PC, 360)
Bioshock 2 (PC, 360)
Grand Theft Auto 4 (PC, 360)
Grand Theft Auto 4: Liberty City Stories (PC, 360)
Oblivion (PC x2, 360)
There's a bunch of game I've picked up multiple times on one platform for coop with my GF, though. RE5 (PC x2) and Borderlands (PC x2) both come to mind, as does the above mentioned Saints Row 2.