uTorrent rocks! If you need one with plug-in ability, try azureus (hope that is spelt right!) azureus has a bit more overhead, but many plug-ins are available.
I use uTorrent as well, but also look at BitComet, which is probably still the most popular. For cross-platform try Azureus, but only if you're not using Windows, as it is a resource hog.
I used azureus ... and have recently switched to uTorrent ... and I have been getting a lot better speeds and lower overhead .... so uTorrent is definitely the best way to go