Hit GameStops early in the morning is all I can suggest.
I got a used Wii months ago on Ebay with Zelda, 6 VC games, 1GB memory card, and an extra wiimote for $350 shipped. Nobody wants a used one since they're so new, so you get a big discount. Seller told me he lost almost $200 on that sale. (!)
First thing in the morning isn't usually your best bet. UPS runs at different times in different places. Ask the Gamestop employees when UPS usually runs, and show up around that time, or shortly thereafter. If you wait until the next morning, chances are they'll be gone.
Just a quick note. I was at Target last week, and there were 5 (yes, 5) sitting on the shelf. Went back a couple days later, and they were all gone. Either people are actually buying them to play them, or they are buying them to stick on the (e)bay. If it's the latter, once the market gets saturated, and they don't bring a premium price anymore, you will start finding them in stores all day long.