Now you know what to get me for my birthday. ThinkGeek is selling thick-looking terrycloth Star Trek robes, in command and science design. They feature the Enterprise insignia on the chest and they have rank on the sleeves (although I don’t know what rank that is on the command robe. The science robe is Commander).
They’re a hefty 50 bucks, but for a true fan who needs something to wear out of the shower, that price is not too high.