You can do it at GameStop.
To be clear, Gamestop is giving $70 for their DSLites. However, you can get more if you still have the box in good condition . . . Walmart will take anything back (and they're evil, so you shouldn't feel bad).
I bought a DSLite last week, but then saw how cool the DSi's were, and returned my DSlite for a DSi.
But I don't understand how a thread about porn is getting derailed. Is it opposite week or something? Do I have to declare a Rule 34 failure in this sector???