µTorrent (or uTorrent) is a lightweight BitTorrent client that supports multiple simultaneous downloads, file level priorities, configurable bandwidth scheduler and speed limiters, even the ability to only run while user activity is detected. Also includes boss key, built-in search function and RSS capability for subscribed downloads.
Note that this software was changed to adware after being added to the Portable Freeware database.
Alternatively, µTorrent Portable is also available, which automatically adjusts paths.