My favorite bolt action rifle is my CZ 527 in .204 Ruger. The next time out I am going to try out my Rem 700 in .243Win that I bought last year. For Semi auto I really like using my ARs in either 5.56/.223 or 6.5 Grendel as well.
Depending on your son's budget I would suggest looking at the Tikka, CZ 550, Rem 700 Sendero, or even a model 7 varmint. I have read good reviews on the Marlin X7/XL7 for budget rifles. No experience with them though.