Slyck
News site with regular articles and statistics on the state of major P2P networks.
http://www.slyck.com/

BigChampagne
Marketing research focused on file-sharing networks, with "TopSwaps" charts of most-popular musical tracks and artists.
http://www.bigchampagne.com

Bitzi
Community-built media encyclopedia where file-sharing users identify and rate digital files, including images, music, movies, and software. Several P2P software provide an option to use this feature to check a file before downloading it.
http://bitzi.com/

Wikipedia: File Sharing
Encyclopedia article covering concepts and issues related to the practice of making files available for download over the Internet and smaller networks.
http://en.wikipedia.org/wiki/File_sharing

File Sharing Talk
Provides information, guides and forums.
http://www.filesharingtalk.com/

PPInternational
A collective for the Pirate Party movement around the world. Offers news and a common resource for international collaboration, and can provide help to form a local party in a given country.
http://www.pp-international.net/

P2P Blog
Blog covering the business, technology and culture of peer to peer. By Janko Roettgers.
http://www.p2p-blog.com/

FileSharingz.com
Provides news, tutorials, detailed guides for each network, client downloads and a community forum.
http://www.filesharingz.com/

Bluetack
A file sharing security solutions portal housing Protowall and Blocklist Manager.
http://www.bluetack.co.uk/

File Share Freak
Provides general information, tips, and tutorials on file sharing.
http://filesharefreak.com/

P2Pnet
Covers news which are relevant to peer-to-peer file sharing.
http://www.p2pnet.net/