JAWBREAKERJAWBREAKERJAWBREAKERJAWBREAKER.
Sorry, had to get that out of my system. But seriously. Jawbreaker. Anything off 24 Hour Revenge Therapy. Boxcar, Ashtray Monument, or Condition Oakland specifically. He will love you to pieces. Really. Really really.
Fugazi is pretty classic, too.
Additional bands to consider:
At the Drive In (One Arm Scissor is obvious, but most anything off of Relationship of Command is pretty good, also some of their older stuff. Basically, choose a song that works well on the mix).
Pretty Girls Make Graves (especially their older stuff, particularly the EP. I'm thinking specifically the song "Liquid Courage" if you can find it.)
And You Will Know Us By The Trail of Dead (anything off Source Tags and Codes is golden.)
BearvsShark
Death from Above 1979
Q and not U (this is sorta iffy. Some of their stuff is very heavy with a lot of distortion and feedback, but it's also very much a refined taste. He may not dig that sort of stuff.)
The Mars Volta (also sort of iffy, they're more progcore or whatever they call it these days but some of their stuff is definitely worth considering. "Cut That City" off the Tremulant EP, "This Apparatus Must Be Unearthed" off Deloused or "Plague Upon Your Hissing"' if you can find it online - it was originally on a GSL compilation disc and that's all - would both fit a relatively heavy, fast mix)
Also, Green Day, Nirvana, Soundgarden, Alice in Chains, Monster Magnet, Stone Temple Pilots, and various other 90's heavy alternative acts should be considered.
You also shouldn't feel ashamed of putting on stuff that's sort of commercialized so long as it's stuff he likes. If he likes My Chemical Romance or System or Alkaline Trio, put some of that stuff on the mix. You don't need to indie it up too bad, remember it's a gift for him to enjoy, not a means for you to flaunt your indie cred.
Pick about 15 bands that fit into that rough general sound, and then pick songs by them all that fit a general theme. If you know for a fact that he has a favorite song by a particular band, put that on there. Don't repeat bands if you can help it, and try to tie the CD together with some sort of theme, whether it's musically or lyrically or a combination of the two.