(picture source: PCWorld)
NewEgg sells them for $300-310 (the higher one includes Thunderbolt). Both come with USB and HDMI. All you need is an mSATA drive and a few laptop dimms. And apparently according to a few people over at tonymac, these are hackintosh friendly.
I am so tempted to pick up a Thunderbolt model. I am very, very, very tempted but I need to justify it.
Here is a youtube video intro
Read more: Intel NUC