The talk of NaNoWriMo is almost always restricted to the purpose of the competition itself: writing. There's a good and obvious reason for that, and I don't feel that I need to explain it. What's looked over most of the time are the artists who are generous enough to create book covers.
To the left you can see what one of the aforementioned generous souls created for my novel. Her forum name is Lauraqua something and donated her free time to do this. It exceeds the skill level I would have put toward it by quite a bit, and as I said - it was free. The quality is pretty much all I could hope for, and this is something that a lot of people would otherwise charge for.
However, the spirit of NaNoWriMo seems to bring out the best in people, as Lauraqua isn't the only artisan to offer their cover design services. There's also Radio-Nowhere, who on top of having a novel to write herself and working a full-time job, offered her excellent services to forum members a month ago. You can check out her work in this thread, or her website. Unfortunately she had to put a stop to any new requests, but the covers she made are pretty fantastic.
There's also the 30 Covers, 30 Days competition, which challenges 30 artists to design a cover for nominated novels. It's a quieter side that doesn't really get much recognition in the flurry of scratching pens (does that metaphor even work? flurry of scratching pens?), but it really should.