rtsam pa: roast flour, flour from roasted grain, 'bras rtsam of rice, gro rtsam of wheat, nas rtsam of barley, this last most common; stirred with water, beer, or tea into a pap, it is the usual food in Central Tibet.
H. Jäschke: A Tibetan-English Dictionary, 1881
As the holder of tsampa.org, I see it as my self-imposed duty to build up a nice repository of material related to this most basic of all Tibetan foods. Currently, this section of my site is embarrasingly small, but my howto on eating tsampa, aptly titled Theory and Practice of Tsampa, has proven fairly popular.
I have also started a listing of places where you can buy tsampa. It is not long, so if you know of anyone else I would be glad to add a link.