[quote name='Lord_Kefka']Second vote for Amazon. Disc Replay. Hell, even Play N Trade.[/QUOTE]
Ditto!
I lived in Wheaton with my family for most of this year (in my own house now though, woo!) and I used to hit up Disc Replay and Play n Trade on a weekly basis.
Half-price books occassionally has some great stuff and I've found some great games at Goodwill too.