I have a small face too, and the Smith Toaster Slider sunglasses are the ones I wear - they're pricey, but have a lot of interchangeable lenses. They're a little bit cheaper if you don't get polarized lenses with them. They have them at REI and at terrybicycles.com (also check out rei-outlet.com for a lot of close-out deals):

http://www.terrybicycles.com/detail....&item_no=74030

http://www.rei.com/online/store/Prod...cat=REI_SEARCH

http://www.rei.com/online/store/Prod...cat=REI_SEARCH