is it a launch 60 with b/c? if so dont trade it in as you will just get normal 60gb price for it, ones with backwards compatability command a bit more money when selling on.
When looking for a slim check your local cash converters if you have one, at the weekend my bro got a brand spanking new 120gb slim for £160 in there. Probly some junkie that nicked it and traded it for cash