mictlantecutli :
...but he is a casual gamer and doesn't want to spend more than 300$.
any help?
It depends on what is meant by "casual gamer." If he plays undemanding games like web-based stuff, Plants vs. Zombies, Torchlight, hidden object games, marble poppers, etc. then he'd be very happy with a HD7750 at most.
If he plays more demanding games (e.g. shooters) just not that often, he's still going to need something powerful for when he does play. Still, from the videos I've seen, BF3 and other modern titles look pretty good even on medium-high settings. I'd be surprised if he "needs" anything more powerful than a HD7850 (which can play at high to ultra), and he may find a GTX560Ti, GTX560, or HD6870 sufficient.
Please clarify what is meant by "casual" gaming, to get the most relevant suggestions.