Digital Blasphemy (perhaps the best known, if not the best artist - although I feel he is both)

Shifted Reality (Artist Juergen Eilts. provides simply out of this world stuff - some of the best 3D graphic work I've ever seen)

PlasmaDesign:
Artist Rob David Randtoul does some fantastic work here.

Savinoff
Another VERY gifted artist, Dmitry Savinoff.  Also has a top notch web-designer, Anton Zhevlakov doing a beautiful job in site layout.

Mike Bonnell   May be the "original"  3D Artist on the Net. Site has a lot of "join now" advertisements but there are some free wallpapers to be had.  Not the easiest site to navigate, but worth a visit

Michaels Place: ".. personal collection of desktop enhancements comprised of original fractal, 3-D, and other wallpaper, background seamless tiles, and desktop icons. Free for you to use on your own desktop or web site." A favorite of my links link exchange partners.

Renderosity:  Great place for 3D artists to pick up tips, graphics, tools, info, etc.  FREE membership.

3D Cafe.    They have a "pay" membership, but still a good place to pick up some free tips and tools.

3D Artists:  Long list of the folks who work in the 3D world.

3D Links ... It is what is says.

Varians: Good place to get textures, info, and other tools.

Terragin.  Pick up your free 3D rendering program here. Planetside offers a limited, but powerful enough to learn the basics while still creating some very nice renders program.