A price range would get you more specific suggestions.
Whatever you decide to go with, I would recommend making sure you get a "real" Windows 7 disk with it, even if you have to pay a few bucks extra.
Make sure you run the Recovery Disk program the minute you take it out of the box. We see people every day who "never got around to it..." and were sorry later. Since your son is a student, Murphy's Law says he'll need it the night before his final exams.
Run a program like PC Decrapifier
right off the bat to clean out all the useless stuff the manufacturer will put on there. Ask for advice if you're not sure what to ditch and what to keep.
Make sure you have a good computer security plan in place; 14-year-olds are not noted for restraint when it comes to downloading "iffy" stuff. (I know, because I used to be one.)
Try to get one that's good enough to play a few decent games - all work and no play makes Jack a dull boy. (And drives mom and dad nuts when he starts telling you that all his friends are playing ___________ and he can't because his computer is not as good as theirs.