There are hundreds of sites on the Web of interest to soccer referees.   Here are some good starting places for ref-surfing:

Metropolitan Washington Soccer Referees Association (MWSRA) Links Page -- Developed by Jim Gordon and Tadd Dawson, this is by far the most comprehensive set of referee links on the Web.  This is as close to one-stop shopping for referee sites as it gets.

FIFA On-Line's Laws of the Game -- Important resource for every referee at every level.

USSF Referee Page -- Official source of information from the national governing body.

AYSO Coach/Referee Information Page -- Official source of information for AYSO programs.

For more detailed and fascinating sites, go to the MWSRA Page.  There's really no point in me trying to keep up with these guys.  For more general soccer sites, check out the YatSoccer Links page.