The Merck Manual (home edition: not too technical)
David Baldwin's Trauma Information Pages
eMedicine Online Text: Emergency Medicine
Emergency Medicine and Primary Care Home Page
Emergency Medical Services for Children
Medical Matrix Emergency Medicine (free registration required)
National Center for PTSD (Post Traumatic Stress Disorder)
Virtual ER: Where Emergency Medicine Meets the Internet
Weekly Web Review in Emergency Medicine
Multimedia Medical Reference Library
Dr. Brackett wouldn't need to use this next site (he knows all these words already!), but it can be useful for us liberal-arts people: Medspeak: the language of ER (Note: as it was compiled by ER fans, some of the slang terms in this list may be more recent than Emergency! vintage.)
In addition, Mary Morris, RN, has compiled an enormous list of medical references at her Code Red site.