I think it kind of depends on your friends but since it's close to the holidays, you might do something holiday themed like an ornament about friendship or a hobby they like.
Snow globe
Picture frame
A little basket, mug or bag of holiday tea/coffee/cocoa with treats
Pretty Christmas nightlight
A book (right now there is a 40% off coupon for borders)
depends what you want to spend. If they are close friends then I would give them something nice like a piece of jewelery, earings. Maybe a mani/pedi at a spa? Something along those lines. I often get those coach wristlets for a gift for people.
maybe dinner gift cert. to their fav. restaurant? if they have children then offer to watch them so they can also have the night out?