Other lower-cost VR systems/groups 

arsbox image ARSBOX (2001)
Built at the Ars Electronic Center FutureLab. A CAVE-like system running on linux PCs, used to forward the center's missions to showcase art and technology and the the Futurelab's mission as the production arm of the AEC. A wall offshoot system uses a pda interface device.
confluxus VR Portal (2001)
Built by the Applied Interactives group, based on research done at the Electronic Visualization Laboratory. One wall system built for museum installations. UIC's undergraduate Electronic Visulization program also has a similar one wall passive stereo system
geowall image The Geowall Consortium
The consortium members pool information to build stereo walls using linux PCs.
"The GEOWALL project makes use of these projection systems to visualize structure and dynamics of the Earth in stereo to aid the understanding of spatial relationships."
SAS cube image The SAS Cube (2001)
A CAVE-like system running on a PC cluster. Developed in France by BARCO, CLARTE, IRISA et Z-A. Claims to be twice as cheap as existing CAVE systems!
VisBox image VisBox
The VisBox is a one wall, fully integrated VR system with head-tracking and passive stereo display.  PC based. Bright projectors. 8' x 8' x 8' aluminum box contains all projection equipment and cuts down on light pollution. Commercially available, especially to CAVEQuakers.
P1 image VizTek
1-6 PC virtual walls, active stereo, tracking, multiple PCs, audio surround. Commerically available.