If you're going to wait, get GT5 now. Especially if you haven't played the first LBP, get that for $20 and wait till LBP2 drops in price down the road. I would wager it'll be around next holiday season that you see any deals on it (other than the B2G1 or the $20 credit from Amazon that happened recently).
If you're willing to spend a bit more (and assuming Amazon's B2G1 sale lasts a few more days), I'd say the $50 GC with 160gb PS3 from Amazon is the best deal. Since you can get LBP2 (57) and GT5 (55) which will net you a free game using their current B2G1, the credit makes this better than Best Buy's deal. So basically, after using the 50 credit, you'll get a LBP2+GT5+another game for 62.