I just added this post to AsianblueX's thread to give some links to the clients in the poll.

Just vote for the client you use mostly. I hope this will give the undecided members here an idea which clients are good.
ABC: written in Python, based on BitTornado v0.2.0, inactive[/i] (last release: v3.1 10-02-2005)
Azureus/Vuze: re-written in Java, client with most features, supports also "Trackerless Bittorrent"
BitTornado: Python, extended version of the official BT client, inactive (last release: v0.3.18 12/23/2006)
BitComet: rewritten in C++, supports all modern features
BT++: Python, based on the official BT client, inactive (last release: v0.5.4 2003-05-07)
Nova Torrent: Python, inactive (last release: v0.3.4 10/25/2003)
Official BT client: Python, latest releases support also "Trackerless Bittorrent"
TorrentStorm: Python, based on TheSHAD0W's experimental BT client, inactive (last release: v1.3 ~2006)
Shareaza: C++ multi-protocol client, supports networks like eDonkey2000, Bittorrent, Gnutella, ...
eXeem: semi-decentralized P2P network which uses the bittorrent protocol (a.k.a. "Trackerless Bittorrent"), eXeem network was shutdown in 2005
µTorrent: C++ µTorrent was designed to use as little cpu, memory and space as possible while offering all the functionality expected from advanced clients.
Transmission: C / Objective C modern BT client for MacOS, UN*X, Windows
Update 2012:
Modern clients support DHT (trackerless protocol), Magnet links, Multi-tracker support, Peer exchange (PEX), UDP tracker protocol, etc.
Recommended clients are: µTorrent, Azureus/Vuze, Official BT client, Bitcomet, Transmission
For more information read Wikipedia:BitTorrent and Wikipedia:Comparison of BitTorrent clients
.