Seventh Kingdom is classic high fantasy LARP based out of the New Jersey area.
The people behind the LARP classify it as an IGE or Interactive Gaming Environment: they are trying to increase the sense of immersion.
The website contains a lot of information about the system and even includes basic info on weapon making and whole lot of background about the different races, classes and environment.
The websites forum is quite active, especially the IC (in character) section.
The system uses a lot of Boy Scout of America venues and to play you actually become a member of their troop. This is great as it allows you to be insured immediately at no extra cost, but for those of you who enjoy a mead or an ale with your LARP you will be in for a surprise as it is banned.
That aside it looks like a well established, detailed and thoroughly enjoyable LARP system!