PSP Go! Show Sony how much you love UMD by taking part in GameStop's latest used games sale. With this in-store coupon, you'll be able to get 20% off any pre-owned PSP games. With coupon in hand, you'll be able to pick up physical UMD copies of classic PSP games -- at a significantly lower price than its digital PlayStation Network equivalent.
You'll have to hurry, though. The coupon is only valid until 9/10/09.