Find out what kind of scotch they like. There can be a big difference in personal tastes as far as single malts go, and while most people will drink most scotch, you can't be sure... People who like the really smokey scotches, like Laphroaig, Ardbeg or Lagavulin may not like the really oaked, toffee-sweet Highland stuff like Macallan. If you're not sure, a nice, neutral bottle like Highland Park, Arran, or Glenrothes is a good choice, and it's not as generic as Glenlivet or Glenfiddich, which any scotch fan would have, and probably be tired of.