If he is not going to upgrade his monitor, he could do fine with a 7870/660ti or less IMO. If he does get a good upgrade to 1440p or more, would recommend a 7970 GE or GTX 680. Possibly a dual card solution if he wants to play newer games and turn up eye candy.
Thing is, assuming no budget, get what is necessary for the monitor he has/will have. If he doesnt upgrade his monitor, $200-$250 would be fine for a budget, while at 1600p I would recomend looking at $700-$1000.