Months ago I used Adobe Air based Twhirl to use Twitter on my Linux machine. However, as an open source enthusiast this application just didn’t fit well in the list of programs I used.
So, after searching around once more I found Gwibber, written in Python and GTK. With it you can attach your Twitter account, plus Digg, Identi.ca, Facebook, Jaiku, Pownce (erm… this last one not for long), and add some RSS feeds for your reading pleasure.
I’m pretty happy using Gwibber. It is fast, light, does just what I want it to in an easy interface. The only feature that I miss is the ability to look at my direct messages.