Honestly, any 15" model with an intel processor is going to be very similar performance wise to one another .
I would try to get the very first model of the 15" unibody that was released in late 2008 (it's the one with removable battery, express card slot and glossy screen). I'm sure you could find one with some warranty left on it for around $1000. Apple sometimes has them on refurb for 1249 (they go quick).. and if there is an update this week, the price will probably drop more.
The only model I would try to avoid are the pre-unibody macbooks with the Nvidia 8600M GT graphics cards (for some reason these are known to have problems that even apple acknowledges). It's just a warning.. you might get one and not experiences any issues with it but I wouldn't take a chance.. I guess with a warranty you shouldn't have to worry about it.
All the unibodies should be a safe bet and the older macbooks with ATI graphics are good (but will be out of warranty). Like I said above though.. try to find the first model of the 15" unibody from late 2008.. you can tell it apart from the other ones because it has a express card slot (instead of SD) and it has a removable battery (instead of built in)
Here is an article that goes over some of the differences
http://www.everymac.com/systems/app...-unibody-late-2008-early-2008-core-2-duo.html
here is the late 2008 unibody that I was talking about on ebay.. doesn't appear to have applecare though. should sell for around $1000 at the end of auction..
http://cgi.ebay.com/Apple-Macbook-P...iewItemQQptZApple_Laptops?hash=item20b0554610