No fuss, no muss. A while back we recommended painting the bottom of an area rug with non-toxic liquid latex Mold Builder to create a grippy layer and bypass the need for one of those no-slip PVC rubber rug liners.
Time reveals better solutions, and we just came across an even simpler approach: Latex Rug Gripper, which is essentially Mold Builder in tape form. All you do is run the tape along the underside of your area rug's perimeter, taking special care not to miss the corners.
$12 for a 25ft roll, available here.