Do they exist?
I'm talking Windows clients here.
In searching for a suitable desktop client I started off with a few requirements. Ideally, the app would post to Twitter & Facebook, and load statuses from both. The only app that I could find that did that was Digsby but I really didn't want an IM client as well. I cut short my requirements to just reading & writing Twitter and ended up with Spaz.
I used Spaz for a few weeks as it seemed adequate but as my development work now requires the running of another VM on this laptop memory is becoming a little precious (even though I have 4GB). I noticed Spaz using 80MB. I have uninstalled Spaz.
I thought it might be due to Spaz' use of Adobe Air so I tried Witty which uses the WPF. That chewed up 64MB before I even entered my Twitter credentials. Uninstall.
Despite its Air-ness, I gave Twhirl a bash as it seems popular. 54MB before login. Uninstall.
Finally, I have settled on the aptly named Bitter. How could one resist a social app hosted on bitterware.com? Its doing a much better job, using about 18MB. My only gripe now is the false advertising - it is giving me less reason to be bitter.
Update: as TweetDeck also appears to be popular I tried it out. 67MB startup. Uninstalled.