Yunhee Kim

Aquafresh White Trays 

"I got compliments after using these―people noticed that my teeth were whiter," reported one tester. The flexible trays, which mold to the teeth, are prefilled, so there's no guesswork about how much whitening gel to use. These trays were also particularly effective on stains between teeth.

Time commitment:
30 to 45 minutes a day for seven days.

To buy:
$38, at drugstores.