I came across a couple of articles to give you someone else's perspective on the top of selecting project management software. I pass them on to you...
Project Management Features Article
This article is from a non-profit perspective, but talks about different types of features - a little different perspective from my most recent posting.
http://www.idealware.org/articles/fgt_project_management.php
CNNMoney.com Article
This article provides some insight into the thought processes of one organization as they selected project management software.
http://money.cnn.com/2009/04/03/smallbusiness/task_masters.fsb/index.htm?postversion=2009040610