Let's collect some useful webpages to this thread. The "Links" section on Bat's pages is a bit... old. :)

BatWiki
(or http://wiki.batmudder.com)
Useful info on large monsters, equipment, areas, races, etc, in Wiki format. Feel free to contribute.

Google Earth map of the BatRealms
A truly excellent map of the entire realm by Jeskko. With a searchable list of areas, guilds, shrines.

World, city and some area maps and area coder info.
Another fine map page by Ggr.

Maps of continents, Pleasantville, Arelium
The original maps by Ooga and a couple of citymaps.

Batshoppe - Monster, eq and room information. ReincSim.
(or http://eq.batmudder.com or http://reincsim.batmudder.com)
A large equipment and monster database. Room location and 'map of surroundings' service.

ZMud triggers
Nice set of Zmud triggers by Flora.

BatClient trigs and trig-creation tool
BatClient resources by Era. A nice boon-calculator.

A large eq list and lots of links
The original eq list by Zithromax. Quality links.

Lots of area and general info
Area information and maps by Dryad. Slightly outdated.

Ordos batpage
Hit messages in order and very very simple reinc simulator that might give decent results.

Precences batpage
Some general info on ships and merchanting and some guild infos.

Milk's Sales Search
You're asking how much?

well what about for quests?

Those you have to figure out yourself. There's of course questroom-in-web.

Quest info pages are not allowed.