IRLP
www.irlp.net
The Internet Radio Linking Project, allowing Amateur Radio repeaters and links to communicate with one another via the Internet, using voice-over-IP (VoIP) technology.

EchoLink
www.echolink.org
EchoLink® software that allows Amateur Radio stations to communicate with one another over the Internet, using voice-over-IP (VoIP) technology.

New England Repeater Directory
www.nerepeaters.com
The most accurate repeater directory on the Internet for repeaters in the six New England states on 29MHz and above.

New York Repeater Directory
www.nyrepeaters.com
A sister site of the New England Repeater Directory above.  This site currently lists repeaters on 29MHz and above in Eastern NY State and Long Island NY.

QRZ
www.qrz.com
A site founded by Fred Lloyd, AA7BQ designed to lookup any Amateur Radio operator's information, with additional interesting features.