uTorrent

This is the most popular BitTorrent client. uTorrent has all the functions a BitTorrent client needs. It has all the downloading and seeding performance of its competitors, but uses minimal resources.

Supports: Windows

Also, uTorrent works fine in Wine. So, technically you can use it in Linux, FreeBSD, Mac OS X, and Solaris as well.

Homepage  -  Download  -  Video Tutorial

Azureus

Azureus implements the BitTorrent protocol using the java language. It used to be the big bully on the block until uTorrent came along and took its lunch money.

Supports: Windows, Mac, and Linux

Homepage  -  Download  -  Video Tutorial

BitComet

BitComet is a BitTorrent/HTTP/FTP download management software, which is powerful, fast, and very easy-to-use. It is a good torrent client, but is losing popularity to uTorrent.

Supports: Windows

Homepage  -  Download  -  Video Tutorial

BitLord

BitLord is a C++ BitTorrent Client. It is a popular bittorrent client that has a built-in torrent search engine.

Supports: Windows

Homepage  -  Download  -  Video Tutorial

Transmission

Transmission is lightweight, yet a powerful BitTorrent client. Its simple, intuitive interface is designed to integrate tightly with whatever computing environment you choose to use. Transmission strikes a balance between providing useful functionality without feature bloat. Furthermore, it is free for anyone to use or modify.

Supports: Mac, Linux, FreeBSD, and Solaris

Homepage  -  Download  -  Video Tutorial