I've never tried one, but maybe a c-shaped vibe like the we-vibe 2 or III. I plan on trying one out soon.
Are you into any kind of kink? What about a light bondage kit?
Massage oils or candles are good...everyone likes a good massage.
You, dressed in a sexy bit of lingerie tends to be a popular gift.
Or, how about a cock ring? They apparently enhance orgasm and lots of men love them.
I don't know! What's he into? There's just so much you get for him!