Since there are a lot of suggestions here, I'd like to add my personal favorite: http://baretorrent.org/
While it does not have all of the features of more heavy torrent clients, it does have a plugin system - although not many plugins exist yet. It's cross-platform, open source, and pretty light. The author has good priorities and is conscious about issues such as privacy, and having good installers that aren't bundled with questionable content.
While it does not have all of the features of more heavy torrent clients, it does have a plugin system - although not many plugins exist yet. It's cross-platform, open source, and pretty light. The author has good priorities and is conscious about issues such as privacy, and having good installers that aren't bundled with questionable content.