I've played a few out here Connecticut way... more specifically between New Hampshire and New Jersey
Realms: (location based targets ie hit in the arm can't use the arm)
CRO: (Connecticut Roleplaying Organization: hp based armor as bonus hp)
LAW: (don't remember the acronym ... but I liked the setup of this one a lot: hp armor was DR complicated for those who can't do math in their heads)
NERO: hp based liked this one less than most others do to the power scale
and currently I'm playing
Dystopia Rising: post apocalyptic Zombie larp hp based armor as bonus hp nerf guns allowed and brand spanking new website here
http://www.dystopiarisinglarp.com/index.php
ther emay have been a couple of others I looked into but those are the ones that stood out the most... well for the Boffer Larps anyway.
Then a whole bunch of other RPS LARPs of the White Wolf persuasion... including the entire list of Camarilla LARPS between 98 and 2002
Aesop
edit: oh yeah the SCA ... well very briefly that's not a LARP... thats a different mindset... some of the people are really nice and cool... some need the services of a skilled therapist and a lot of meds... I have some friends that are on one side ofr the other of that line, but I couldn't really get into it. Attended a couple of events in the NE though