Description:
The Fort Hays University (USA) soil ecology links page has lists of links categorized by main classes of organisms and is especially strong in soil macrofauna, from centipedes to ants to slugs

Accessible from:
http://www.fhsu.edu/agriculture/soilsecologywebsites.htm

Description:
This website is a very readable description of the functional groups of micro- and macro-fauna in the soil, and their role in the soil ecosystem.

Accessible from:
http://www.agroforester.com/overstory/overstory81.html