Keri in Eight Days a Week (a highlight of the 1997 Slamdance Film Fest), one of the sexiest non-nude scenes.
Some other great scenes that come immediately to mind in the non-nude category:
Halle Berry in Swordfish (2001). That film also has a topless scene, but this underwear scene was the highlight for me.
Jamie Lee Curtis in True Lies (1994)
Joy Patricia Harmon washing the car in Cool Hand Luke (1967)