This is an easy one.....
http://www.socialoomph.com/95917.html
Social Oomph is different is that it allows me to build queues for all of my postings regardless of if they are going to Twitter, Facebook, etc...
I am able to schedule these hourly, daily, etc....
It's been working great for me as I post to about five different twitter accounts, facebook, etc... Using this tool allows me to manage and schedule all this from one place.