Here is the Advisory Circular link.

http://www.airweb.faa.gov/Regulatory...del%20aircraft

Note that it is not a regulation and not a requirement. I know I thought it was at one time but it is not. Note it states voluntary compliance.

Here is the reg used for model rockets, moored ballons, and kites.

http://ecfr.gpoaccess.gov/cgi/t/text....2.9.2&idno=14

Note that the limit is 500 feet but it is a regulation that requires a waiver when flying above that altitude.