Online Technical Writing: Online Textbook - http://www.io.com/~hcexres/tcm1603/acchtml/acctoc.html
Extremely useful information, a number of model documents.
Direct links to some of document models (based on the course "Introduction to Technical Communications" taught by David A. McMurrey at Austin Community College).

Online References for Writers. Dictationaries, encyclopedias, etc.
http://www.cs.cmu.edu/references.html

Guide to Grammar and Writing
http://webster.commnet.edu/HP/pages/darling/original.htm