Jim:
Take David K's advice -- if you're on the A9, Boat of Garten is a ridicously easy detour (5 minutes at most?) off the main road, and yet the course has a wonderful isolated sense of itself -- you, the course, the mountians and the Spey River, that's it. Of the central Highland courses mentioned -- Newtonmore, Kingussie, Aviemore -- the Boat is the far superior. A really good course.
One other -- again, very close off the A9 near Stirling -- is Melvyn's recommendation of Bridge of Allen, a wee 9-hole course that nonetheless was designed by Old Tom Morris and is faithfully maintained to its original design, from reports. Again, very convenient off the A9, and a round there couldn't be more than 1-1/2 hours.
A word about "detours" off Scottish roads (which influences my recommendations) -- what may appear to be on a map as a "short" detour can often be quite lengthy, time-wise. There is little that is quick in getting around Scotland (one of its joys, actually) unless you are on the main highways. It's your time, of coure, and I don't mean to deter from many of the fine recommendations here. But you'll spend at least half a day getting to the coasts from your central route planned here.