What would people recommend as a free (as in freedom) BitTorrent client on Linux? Wikipedia has a Comparison of BitTorrent clients. For the record, I'm currently using QBittorrent, which I'm quite satisfied with, as of recent versions, which are nicely featured and stable. I'm currently running 2.6.7 on Debian Squeeze. The version on lenny (1.1) was a bit dodgy, but the project was quite young then.
However, it does not hurt to learn what else is out there. I'm quite partial to Python software, if any Python BitTorrent clients exist. QBittorrent is written in C++. Many of the most popular BitTorrent clients are proprietary, judging by the Wikipedia page.
EDIT: Thanks for all the recommendations. If the recommenders would like to explain why they like their preferred clients, I'd be happy to hear it. I know very little about what makes a bittorrent client good and would be glad to be educated. Also it would be nice if something could be said about Linux distribution support and possibly other OS's like FreeBSD and OS X, though I only use Debian and am unlikely to change.