*THIS THREAD IS OUT OF DATE - PLEASE USE LINKS BELOW*

Main site: https://www.ethereum.org
Forums: https://forum.ethereum.org
Github: https://github.com/ethereum

Blog: https://blog.ethereum.org
Wiki: http://wiki.ethereum.org
Meetups: http://ethereum.meetup.com

Whitepaper: http://ethereum.org/ethereum.html
Yellow Paper: http://gavwood.com/paper.pdf

Facebook: https://www.facebook.com/ethereumproject
Youtube: http://www.youtube.com/ethereumproject
Google+: http://google.com/+EthereumOrgOfficial
IRC Freenode: #ethereum (http://bitly.com/IRC_ethereum for weblink)