Hollywood Video is currently having a great sale on their used games. All $29.99 and under used games are being sold for $4.99. Just be wary that this is a YMMV sale. If your Hollywood Video has a Gamecrazy attached to it, you will probably not see this deal. Call ahead also as some Hollywood Videos may not currently be running the promotion.
Also as a collectors notice, some games may be in Rental Condition. The oddest ones are obviously the GCN games. I got them with instruction manuals and the actual cover in a generic DVD case. DS games will probably be the best value if they come in a case since they usually were traded in.
Also, your prices may vary from store to store. Some guy got MGS4 for $4.99, while my Hollywood Video was selling it for $34.99 making it ineligible.
Happy hunting.
Edit: Just want to mention that I was wrong about the pricing thing. If a game looks like it is priced to high, it probably is. As an example, the MGS4 I saw was actually $4.99 despite the price tag being wrong. Feel free to ask for price checks.
Now onto my personal grabbings:
Excite Truck, New Super Mario Bros., Mega Man X Collection, Pikmin (GCN), and GTA IV (PS3). My friend is scolding me for not buying Bioshock for 5 bucks.