A writer is only as good as his arsenal of "weaponry" allows him to be.  Aside from our own mental acuity, verbosity, and general drive, there are plenty of online tools that can help us be the best writers we can be.  To that purpose, here are some of the best links I've come across on the web.  By all means, though, feel free to add links of your own that you feel other writers would benefit from!

Multi-Purpose

LitLift

A neat little website that helps you organize ideas, character information, and other snippets of information vital to formulating a good story or novel.

Acrobat

Their online word processor is, hands down, the best I've had the pleasure to experience.  It doesn't hang or choke on large documents, you can share it out to specific people for critique, and access your stories from any computer with internet access.

Wikipedia

Never underestimate wikipedia as a good source of information and fact-dredging.  While it is updated by users and some of the information can be out-dated or accurate, it usually makes a good go-to place for alternate sources/articles related to the topic you are researching.

Thesaurus and Dictionary.com

A good thesaurus and dictionary are both a necessity in every writer's arsenal!

World of Warcraft Specific

Wowpedia

The online source for all things lore for World of Warcraft and the Warcraft Universe.