CSS Nav File Related
www.turtlerockstudios.com. Home page for Turtle Rock Studios, creators of the wonderful CSS bots. Sadly the support forum on bots they used to run has gone, but you can check out what TRS are now working on.
www.csnavcentral.com. Forums, naving guides and downloads available at this very useful site, including lots of stuff for CS:CZ.
www.fpsbanana.com. Shed loads of maps so a good chance of finding what you're looking for, but the blunderbus approach means there's a lot of dross along with the gems.
www.lanmaniax.com. Opposite style to fpsbanana with a relatively small collection of maps but usually of a high quality.
www.cstrike-planet.com. Well organised site with a good selection of maps.
www.dimensionstudios.org. Map creation studio so only a small collection of their own maps, but all are of a high standard and most come complete with a Barndoor race tuned nav file.
There are of course many other sites offering maps but these are my current favorites so should carry a lot of the maps for which I've done navs.