Sonata Arctica - Silence
Within Temptation - The Heart of Everything
Stone Sour - Come What(ever) May
Given he likes Disturbed, Nightwish etc, the bands above might interest him. Sonata Arctica and Within Temptation are in the same direction of music as Nighwish, but in different veins, whereas Stone Sour is a heavy rock band which varies from growl (the main singer is lead singer of Slipknot, but I rate Stone Sour far higher than Slipknot due to thier more varied etc sound), to well thought out, gentler, but very touching songs like 'Through the Glass'.
Also, if hes into that sort of music, and he doesnt have it, you really got to get him:
Metallica - Metallica (The Black Album)
I'll also agree with what was said earlier that he might like Trivium, but I'd personally not get him the last album as it was thier weakest one IMO.
He might also like Evanescence - Fallen (thier latest album again is the weakest so far, at least IMO, so get him Fallen as its got a lot of the 'classics' on it). Evanescence (if you don't know them), are kind of like a mix between Nightwish, Sonata Arctica and Within Temptation, being the more 'mainstream metal' of those 4 bands.