Uhhhh Lego Batman PS3 used at Gamestop isn't a terrible flip. It's 17.99 before edge and 10% discount. Trades in for 14.50, 360 version for 14.00. You will only lose a couple bucks per copy.
Just about everything else has been updated since the program started so there aren't a lot of amazing flips. Oh! You could also try and pick up Gran Turismo 5 Prologue. It clearanced out at my Target for $10 and it trades in for I think 10.50.