I am in a constant struggle with the circles under my eyes. Even with a full 8 hours (which I haven't gotten since grade school) I still wake up looking like Brittany Murphy in Spun. Thankfully, GlamTV has released a how-to video for covering annoying under-eye circles.
The makeup artist advises you to start with a regular concealer (I'm partial to Clinique All About Eyes, $15.50) from the crevice out to the corner of the eye, and then layer a highlighter like YSL's Touch Éclat ($40) on top.
Check out the video for other nifty tips, and you'll be well on your way to looking like you actually sleep once in a while.
And visit Real Simple for more ways to keep dark circles at bay.