Alot of times the best thing you can do for a depressed person is let them be. Alot of times they just need to "change the channel" in their minds. And because depression comes in waves, it must be endured. For me, I like to take walks or get some form of exercise because it elevates my mood; although sometimes when you're depressed you feel fatigue so you don't want to do anything.
Give him space, let him approach you when he wants to, and try to not act like you feel sorry for him; just tell him "it will pass" and carry on until he starts to feel better.
As far as medication goes, alot of them have side effects that sometimes seem as bad as the depression. I like the old tricyclic medications; their primary side effect is sleepiness whereas the newer types an antidepressants seem to have alot of strange and uncomfortable side effects that make it hard to take. The one exception is prozac, which i think is ok, but for some people it can make you have trouble sleeping.
I'm sure this was little help, but I've suffered from depression myself, still do, and I wanted to offer some advice.
Brian