These are some of the sites, created by Discworld players. You can find more full, but uncathegorised list here

Geography

Discworld is big. It has over gazillion unique locations! When you need to find wehere the Sek you are now or WTS is that street/city/continent you need to get to, maps, created by players, are your best friends.

Most well-known maps page is Airk's atlas. It has maps of about everything, except wilderness. Bad thing is that he got WoWed lately, and don't update maps anymore. If you want more (likely, most) up-to-date versions of that maps, visit Kefka's site. Only drawback of Kefka's site is that it seems to be offline occasionally, so you may prefer to download his maps, just in case.

As about wilderness, Boots maps are unrivaled. He has very precise maps, containing about every square mile of in-game parts of disc (and man, there are lost of them). He has cities maps as well, not as up-to-date as Kefka's, but a little more informative and thorough.

Other maps of terrains can be found on Peta's page. They are not as thorough as Boots, and not as insanely huge.

If you need maps of some more obscure places, like Genua sewers, Grflx caves, try Zuroc's maps. There are lots of interesting maps there, and only drawback is that this site uses jscript aggressively, which can be buggy on some browsers.

You can find another interesting map page on Thieves guild page. They are old, and not very user-friendly, but has very interesting pieces, like precise-to-location map of SUR terrains, or map od Bes Pelagric complete with black market