Hi,
I would recommend ActiveCollab as it can be both used for small and big businesses. Also, it's been tested for years now and for me, it has all that capabilities to manage your business easily plus giving tasks for your team. Here are some features that I've found:
-It's got project milestones
-Discussions
-File sharing
-Joint calendars
-Time tracking and forums
It is also very handy that it lets you export your calendars to Outlook, iCal, or Google Calendar. Another nice touch is being able to work from your mobile including Blackberry, iPhone, or other XHTML enabled mobile device.
Additionally, you can give your clients their access for them to also see the accomplishments of the projects as well.