From Forbes.com:

Today, Botox, which costs about $250 per treatment area, isn't used just for zapping deep forehead wrinkles, according to Nikolov. It also works to prevent stains around the underarms by stopping the glands from producing sweat. About eight to 10 injections of Botox in the area can do the trick. "When you're on the red carpet," he says, "you look great, and maybe you're a little nervous--no matter what, the last thing you want is to get perspiration on your gown."

To prepare for their close-ups, some stars turn to cosmetic dentists for power bleaching, says Miami-based cosmetic dentist Jorge Blanco. Patients pay $500 to $1,000 for the procedure, which is done two and a half weeks in advance of an event. Blanco applies whitening gel to the teeth, then sits the patient in front of a light that promotes absorption for about an hour. Sensitivity may be a problem for a day afterward. Some dentists send people home with teeth-whitening trays and solution so they can control color all the way up to an event.