Here is a list of currently active Quake communities, portals, software and other miscellaneous sites which have helped or inspired me.
The Quake community as a whole is very fragmented, so lists like these help to bind it all together in some way.
This list isn't comprehensive by any means. Bear in mind also there are other Quake communities (like bulletin boards/forums) that were once active that have seemed to have become dormant over the years. I won't list those here, but there is some goodness and historical perspectives on things in the ones that are still online if you look hard enough.
Oh, and I hear there is a strong Quake Discord community, but I can't really comment on that kind of newfangled stuff.
- Quaddicted (Most of the best (and worst!) maps ever are compiled and hosted here. Great forum community too.)
- Func_Msgboard (An odd messageboard layout, but by far the most active.)
- Quake Wiki (.org) (An excellent reference for how Quake works.)
- Quake Wiki (.net) (A great community resource in its own right.)
- QuakeSpasm (A modern engine for Quake with compatibility with modern Windows, Linux, BSD and Mac.)
- Trenchbroom (For creating Quake maps. It's the best.)
- The Quakecast (The one and only Quake podcast with dumptruck_ds. Very insightful topics and guest with some of the most important and influential people in the Quake community.)
- dumptruck_ds on YouTube (Excellent Trenchbroom tutorials.)