ER Live I haven't had a chance to check this out yet, but from what I hear it's really cool.
MedSpeak Alphabetized Definitions of All the Medical Words You Hear on ER
1 2 3 Three ER Drinking Games Try it with caffeinated drinks instead of alcoholic ones for you under-age ER fans (like myself).
Roger's ER Page Voted One of the Top 10 ER Pages by Total TV Magazine cute background, ER chat, some sounds (including the theme song) . . . definitely worth your time
The ER Homepage Also voted one of the top 10 ER pages, this not-quite-modestly-named page has it all: sign up for the mailing list, check out the ER FAQ, a few pics, lots and lots of quotes.