What are YOUR needs?
What is the size/duration of your projects? How many documents of what kind do you need to manage? How many staff do you have and what types of things do you have to workflow? How often do you and your staff or clients need to work together on projects?
The most useful tool is the one that helps your business run more efficiently.
I'm doing a little research at the minute and would like to get your opinion of which of the following software solutions is most useful to businesses (in a web environment):
Project Management
Document Management
Business Process Management (Workflow)
Collaborative Working
And comments would be appreciated.

Chowhound
Comic Vine
GameFAQs
GameSpot
Giant Bomb
TechRepublic