If you want to look pensive or monastic, a shaved head looks good on most men, especially men over 30. It's a risky cut (some people quite plainly have ugly heads, like
Placido Polanco), but really, it does look good on most men of a certain age. Young men can do it too, but you have to have the right clothes to pull it off or else you'll come off like a skin-head.
The Robert "Fat Bob" Smith style rat's nest is always popular as well, though, often high maintenance.
Keeping the hair at 2-5 inches and slicking it back is a simpler style, and timeless. Good especially for men with a widow's peak hairline, or high, pronounced foreheads.
More to come, maybe.