Asana is making a name for itself in the world of Team and Task management. For a very good reason; Asana Rocks!
Free flexible, ubiquitous, powerful, and did I mention free, well I mean mostly free.
Asana has taken a very practical and easy to follow approach to task management on a team wide scale, it works for personal task, business task and every task in between.
It works in every OS, and platform, as it is entirely web based (although there is an iPhone App, which is pretty good!)
I will take you on a brief tour of Asana, enough to convince you to give it a shot!
Try Asana here.