it depends.
for me the most valued physical thing ( there are things much more value than any physical gift) is the cards she gave me in the special days (b'day, aniv) which she hand made just for me. I love them so much. then her hand made gifts (cross stiches, ribbon flowers etc).
if you plan to give this periodically for long time then select some thing valuable for his day to day life and tell him that you'll give it to him every year. my gf gifts me my wallet for my b'day. I like that tradition.
it all depends on the person. if he is a nerdy type may be some electronic will do.watch, ipod etc. some people like cloths but to that you have to know the exact taste.