Depends on your budget of course. If money was no object I'd buy myself Assos. If you can't find a sale they are stupid expensive. Others like Castelli, Capo, Pearl Izumi, etc. are quite nice. But, as others have suggested it really depends on what fits him best.
http://www.competitivecyclist.com/as...AAS001U-RD-TIR
FWIW I have Assos bibs in black and a pair in white. Both excellent. Although white does get.....attention.