Identification, Images, & Information
For Insects, Spiders & Their Kin
For the United States & Canada
From the welcome page:

The Arachnological Hub of the World Wide Web for the study of arachnids (spiders and their relatives)
Acari - Amblypygi - Araneae - Opiliones - Palpigradi - Pseudoscorpiones - Ricinulei - Schizomida - Scorpiones - Solifugae - Uropygi ( Thelyphonida )

Basically a portal with lots of links to other sites of interest (including this site).
http://www.arachnology.be/Arachnology.html