General Information:

Amateur Radio Relay League: The National Association for Amateur Radio – Online community of amateur radio operators. Offers call sign look-ups, forums, equipment trading and news.
eham – Online source for product reviews and articles by amateur radio operators.
APRS – Learn about Automatic Packet Reporting System (APRS) to facilitate position tracking and messaging. – View APRS stations and their locations around the world.
Logbook of the World (LoTW) – A service provided by the ARRL for the electronic confirmation of or contacts.  May be used to confirm contacts for ARRL sponsored awards. – Service that can be used to electronically trade QSL cards.
SD Link – The South Dakota Link system is a series of linked UHF & VHF repeaters across the state for use by radio amateurs.
QRP and Homebrew – A site for information about QRP and HomeBrew.
The History of Telecommunication – General history of telecommunication technologies from ShoreTel.
Storm Spotting at Home – A good collection of resources to learn about weather and storm spotting.

Audio / Video:

My Amateur Radio – Jerry Taylor, KB0BIK, hosts the monthly Practical Amateur Radio Podcast (PARP) covering a variety of  amateur radio topics.
Ham Nation – (on the TWiT Network) is a weekly video podcast hosted by Bob Heil and covers a variety of topics.
Amateur Logic TV – Amateur radio technical video podcast.
Amateur Radio Newsline – A weekly audio podcast covering current amateur radio news topics.