As far as processors go; since I primarily use LuxRender(or should say "only use luxrender"); I went to their wiki and to the benchmarking chart.  Then just started at the top for performance and went down the list until I got to a cpu I could actually afford on my full-time-student-with-a-wife-and-five-kids budget.  That landed me at the AMD Phenom II X6-1090T.  It's luxrender scores were pretty outstanding for the price and it's cheap enough I might be able to afford to rebuild the wife's puter too.  As far as vid card goes; luxrender seems to work better with amd cards specially since I do a lot of gpu rendering.  For the measely 129 pricetag, the HD7770 is a pretty darned good card; unless you have the cash to dish out for a mid to high level firepro card.