qBittorrent

Simultaneous download of multiple torrents
Integrated torrent search engine
Integrated RSS feed reader and downloader
Good internationalization
DHT, PeX, Encryption, LSD, UPnP, NAT-PMP, µTP
Cross platform (Linux, Mac Os, Windows)
Very lightweight
Torrent queueing and prioritizing
Control over files in a torrent (filtering, prioritizing)
Nice µTorrent-like interface with Qt toolkit
IP filtering (eMule dat files or PeerGuardian files)
Peer display with country and hostname resolution
Advanced control over torrent trackers
Closest open source equivalent to µTorrent
Torrent creation tool
Remote control through Secure Web User Interface