The websites that in my opinion are essential browsing for any WFRP fan.

Bergsburg Project
An amazing example of what a community project can achieve.
Black Industries
The official site for the second edition of WFRP.
Critical Hit
An excellent selection of articles about the Old World.
Le Grimoire
The French language WFRP magazine.
Mad Alfred
Alfred is one of the more prolific authors for WFRP and has his unofficial material here.
RPG Archive WFRP Scenarios
Many of the finest unofficial WFRP v1 scenarios collected in one place.
Strike to Stun
On-line magazine for WFRP with new background, scenarios, reviews and loads more.
Strike to Stun Forums
Home of the WFRP communities most active independent forums.
Tim Eccles
Author of the unofficial Private War campaign and organiser of the TimCon WFRP conventions.
Warpstone
Website for the excellent Warpstone WFRP print magazine.

The best of the rest in alphabetical order.

Alphonse Nitpicker
Archive Skaven
Atoom's WFRP Resort
Castle GoblinStein
Creative Fantasy Edge
Dave Sherohman
Dragonscroll
FantasyLand
Graeme Davis
Jason Hiltz
Joxer's WFRP Site
Marienburg Project
Regiments of Renown
Roysten Crow
The Chaos Library
The Snotling Foundation
Tilean City States
Wandering Mind
The WFRP Collection
WFRP WebRing
Schwartz Filez
Warhammer Mikpage
WFRP Burrow