I don't routinely hit the big chain places. I perfer the smaller locally-owned places to buy, but their trade in values are usually awful(seriously, one place gives $4 for a Dreamcatst system then tags them at $80) .
The local Movie Gallery has started dealing in new and used with trades though. Saw RE3 for GC for $13 the other day... GS GIVES $14 for that game and sells for $30-$40.
BTW, Game Crazy is selling the GC OOT bonus disc for only $25. Most places want double that. Pity I hated how the game played on a GC controller or I'd have jumped on it.