MacBook Pro that runs Snow Leopard
Apple lists all software versions that run on models here:


Mac OS X versions (builds) for computers - http://support.apple.com/kb/HT1159


So you could focus on models that shipped with Snow Leopard and perhaps look at even older models that meet the minimum system requirements for Snow Leopard.


Mac OS X v10.6 Snow Leopard - Technical Specifications  - http://support.apple.com/kb/SP575