Etsy.com is a fantastic little website. It's a place for artists, designers, clothes makers, etc. to sell their home-made goods. I've been buying stuff off it for the past year or so now. It's a great resource for affordable art. Unlike Ebay, you're not competing with another anonymous bidder, and most sellers will ship worldwide fairly cheaply. Now and then, I'll post some good Etsy finds. It may be too late for Christmas, but it's never too late for good art!
Ashley G. is popular artist, both on the site, and in many other design blogs.
I own a couple of prints from this gal, Stawberry Luna. Beware when buying from her, however, as she likes to send little gifts of finger puppets, stickers, and candy in with your order.
The Black Apple is another of my favourite sellers.