uTorrent is an efficient and feature rich BitTorrent client for Windows sporting a very small footprint. It was designed to use as little cpu, memory and space as possible while offering all the functionality expected from advanced clients. With uTorrent, you can download files faster and contribute by sharing files and bandwidth. Additionally, uTorrent supports the Protocol Encryption joint specification (compatible with Azureus 220.127.116.11 and above, BitComet 0.63 and above) and peer exchange.
Thanks to kabino and Astron for the update.