Azureus

Azureus is a Bittorent client with many significant features and upgrades not available in the original program. (If you don't know what Bittorent is, read the first article in this series). Azureus allows the user to download multiple torrents in a single GUI interface, which can--thank god--be minimized to the System Tray. The program also allows detailed options, information and configuration. While downloading a torrent, you can see:

• which files you've downloaded
• what percentage of each file and piece you still need, the piece number and availability
• who you are downloading from, their download and upload speeds, their IP, their port, their client and more options if you are Super-Seeding
• Time remaining, download and upload speed, time remaining, file and tracker information.

With Azureus you have complete control over your download. You specify your max upload and download speeds, how many simultaneous connections you want in each direction, server information-including an option to manually input your IP address if your NAT/firewall hides it, seeding rules, filters (although the RIAA and MPAA haven't really bothered Bittorrent users YET), stats and more.

And it looks great, too

Its probably one of the best clients out there. Download here. It works with Java Web Start, so you need to download that too.