An obvious one would be a
Tilt digital hydrometer - it''s a "want" rather than a "need" in as much as it doesn't really do a lot more than a $10 glass one, but it's cool being able to monitor your fermentation in realtime. They've only been out a year or so, which means there's a good chance he's not got one - and even if he does, if he's serious then he'll probably have more than one fermentation on the go. So it's something that would work pretty much regardless of what his setup is, and it has a bit of "cool" to it, particularly for a child of the iPhone generation.
I can appreciate that the following may not work because if you're about to leave college then he's probably going to be living in a rabbit hutch for the next few years. But if he does have room at say his parents' house for some bulky gear, then something like a stainless steel fermenter would be something that would last him a lifetime and would be useful pretty much regardless of what brewing he does - fermenters are often the limiting factor on how much brewing you can do. And you could get the outside (not the inside!) engraved with something that means something to the two of you, daft or profound depending on your relationship.
On a similarly bulky note, if he likes his big dark beers then an old bourbon barrel for barrel ageing would be appreciated - but it doesn't really work as a surprise, you want to have beer fermented and ready to go in it to avoid it drying out.
More realistically, it might work better to fill his head rather than his parents' garage. There's all sorts of beer-related courses available, some leading to qualifications and others more for fun. And certainly over here, some small breweries offer "brewery experience days" where you get to help them brew beer on bigger kit than your standard 5-gallon homebrew kit! It would be something fun for the two of you to do together, and you'd probably also get a keg for the end of term party....
On a related note, off-flavour training kits are about $150-ish I think and are the sort of thing that would be appreciated by the more serious homebrewer.
I'd probably go with either the Tilt or the brewery experience day.
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