FCC:
Home of the Federal Communications Commission.

FCC Rules:
Part 15 and other rules.

Industry Canada:
Canadian Rules (RSS-210, RSP-100)

Low Power Radio Association:
Check out their Links for various International Rules and
Standards sites.

Radio Authority of the United Kingdom
UK Licensing Information and Rules

Alex-X Electronics Toolbox
A great reference site for hobbyist or professional.

AMSAT:
AMateur SATellite national organization, Washington, D.C.

ARRL:
The Amateur Radio Relay League, one of the oldest electronics
groups, worldwide. Mostly "Ham" related stuff, but good all the
same.

Radio Amateurs of Canada:
Information on "Ham Radio" in Canada.