First off it really depends on your machine... if you can handle the top cards or not (or should i say, you may buy a "top-of-the-line" card, but your machine can't let it perform at 100%, when you could get the same performance, your machine limits these cards to, in a cheaper card)... Your CPU/Mobo, RAM and PSU for the most part.
Here's a list of the "considered" Top 10:
1 GTX 295
2 HD4870 X2
3 HD4850 X2
4 GTX 285
5 GTX 280
6 9800GX2
7 HD4870 1GB / GTX 260 Core 216
8 HD4870 512MB
9 GTX 260
10 HD3870 X2
That wouldn't be the case if he's playing AoC lol. Its best to find out exactly what games hes playing. I would assume probably WoW but it could also be CoD5 or anything like that. I know they aren't terrible demanding games but a better card is worth it for those games