Lunaran (http://www.lunaran.com/)
- Maps (http://www.lunaran.com/page.php?id=4)
- Textures (http://www.lunaran.com/page.php?id=8)
- Stuff (http://www.lunaran.com/page.php?id=9) - contains texts about mapping
Stolen from Lunaran's inspiration section:
- Opacity (http://www.opacity.us/)
- Sleepy city (http://sleepycity.net/)
- Urban atrophy (http://www.urbanatrophy.com/)
- Zahkunst (http://www.zahkunst.net/)
- ru_abandoned (http://community.livejournal.com/ru_abandoned/)
Alientrap (http://www.alientrap.org) links page (http://www.alientrap.org/forum/viewtopic.php?t=9).
More later.
We can, of course learn from the bigger quake mapping community
http://www.quake3world.com/forum/viewtopic.php?t=290