(FORTUNE Magazine) – You've heard of It Girls, but what about the fashion equivalent--It Bags?

Here's the drill: Each season's It Bag must be wildly expensive, on the arms of beautiful people, and pretty much unavailable to mere mortals.

Past must-haves include Fendi Baguettes and the horn-handled Mombasa by Tom Ford for YSL, but lately Louis Vuitton has been on a streak. Last year's bright Murakami bags were so hot that Jessica Simpson took one camping on her MTV show Newlyweds. Murakami sales have reportedly surpassed $345 million, helping to boost Vuitton's U.S. sales 38% in 2003.

This spring Vuitton's gold, ostrich-trimmed "Theda" (above) seems to be the latest hit--the $3,550 bag has been snapped up by Sarah Jessica Parker and rapper Eve and has a one-month waiting list. Scarcity has certainly boosted the bag's allure, but Marc Karimzadeh, an editor at Women's Wear Daily, says there's another benefit: Once in the store, women are "much more prone to spend the money on something else." --Kate Bonamici