Official BitTorrent Home Page – simple client and docs.

The Poor Man’s Tivo – great intro to BitTorrent

infoAnarchy’s Wiki – overall reference

TheRegister’s BitTorrent analysis

Azureus – Java based, generally recognized best client

Blog Torrent – simple tool for hosting .torrent files.

BitTorrent for Blogs – Jeremy Bowers post on RSS and BitTorrent.

Top 10 Bittorrent Sites – BitTorrent search engines.

Not directly related:
ITConversations – technologist radio show podcasts.

BlogBridge – Java WebStart RSS reader.