HootSuite is a professional social client, featuring various platforms: Twitter, Facebook, Facebook Page, LinkedIn, Ping.fm, WordPress, MySpace and Foursquare. I presented you some time ago Seesmic's web service (here), and the main difference between them is that HootSuite is much more complex and supports other platforms, not just Twitter.
There are many things you can do with HootSuite: track results of your websites (only for WordPress), add contributors to your account (who can post from your account), schedule posting at certain time/date, monitor mentions or assign tasks to your contributors. All those in a well organized screen, with a theme of your choice (you have 3 themes to choose from).
Posting is done easily with a large number of options, and with the option of selecting the network on which to post. If you are confused about changing settings, viewing your stats or managing plugins, just hit that owl on the upper left corner of the window.
Go now on http://hootsuite.com/, create an account, and start using all of your social networks from one single place.