The only social media client I have installed in my laptop is TweetDeck (the same one I used in my iPhone and iPad) but it looks like Seesmic Desktop 2 is going to replace it already.
Seesmic D2 allows you to manage over two dozen social media accounts and web services — from Facebook and Twitter to FourSquare, LinkedIn and MySpace or Ping.fm — just one social client to rule them all.
And that’s on top of the iPhone and Android clients already available.
Best part of it is that developers can create their own plugins to extend compatibility to other services or sites.
Seesmic runs on Adobe Air so make sure you have it installed before downloading the desktop client {download}.
The old Seesmic Desktop and twhirl runs on Air, while the new one (SD2) runs on Silverlight :D