People have asked me for recommendations regarding where to buy the newer small form factor, so-called "mini" or barebones computers. At this time I cannot recommend any particular vendor but can point you to some useful links. Here I'm emphasizing the mini-iTX scene although the mini-ATX boards have as big a following.
Viarena -- People ask me where can I get a small motherboard, specifically the mini-ITX. Here is the Gospel site/store for all things VIA mini-iTX. Links to just about everyone worldwide who has anything to do with this form factor.
Mini-iTX -- Of course the list would be incomplete without listing the top enthusiast site for mini-iTX.
Directron -- Sells preconfigured mostly slow Intel boxes in groovy looking cases
Case Outlet -- Great site for cases, many with chipless motherboards...best prices
Checkercube -- it seems as if everyone sells the boxes from these folks.
Shuttle -- Here are the guys selling one of the most popular boxes complete with nVidia technology built-in.