"Sous vide" is French for "under vacuum" and cooking en sous vide typically refers to vacuum packing ingredients, then cooking them under very strict temperature control. "Precision cooking" might be a more accurate term, but all gastronomical things tend to gravitate toward the French descriptions. When sealed in plastic, the aromatics cannot vaporize so flavors are more intense, and food can be cooked in water baths held at specific temperatures for long periods of time without the water soaking or otherwise changing the texture of the food. Sous vide is a food service technique that has been embraced by the world's best chefs, and with some equipment that is not outrageously expensive, you can duplicate some of their dishes.
My two favorite references for sous vide are Thomas Keller's Under Pressure and A Practical Guide to Sous Vide Cooking by Douglas Baldwin.
Here's the short form of the recipe:
Salt and vacuum pack as many beef ribs as will fit in your water bath (I prefer grass-fed beef).
Cook at 135 F for 48 hours.
Sear with propane torch.
Eat immediately - sharing is optional.
Step 1: Sous Vide Equipment
Sous Vide Magic PID temperature controller purchased from Auber Instruments on Ebay
cheap crock pot1 without electronics (just an on/off switch)
FoodSaver Vac 200 (the link goes to a model that's close enough) Vacuum Sealing Kit (borrowed from helava)
Update: since I purchased my equipment, Sous Vide Supreme has started making an all-in-one unit designed for home use. The regular 10L unit is $400, and the still-quite-roomy 8.7L Demi is $300 - comparison here.
1 A rice cooker or electric kettle can also work; the variables are size of container, and speed of heating. I usually pre-heat the water, as crock pots heat up VERY slowly. We've got an industrial-sized rice cooker on order. The key is to make sure your heating device doesn't have a brain, as the PID controller works by cycling the power on and off and you can't be resetting your crock pot each time.