We use 37 Signals' Basecamp for all of our project management. (in fact we use all of their products - we're huge fans). Basecamp lets us keep project milestones, to-do lists, and messages in one central location. This means you can log in and see the status of your project at any time. Our team members are also available on the built in Campfire chat within Basecamp, ensuring quick answers to your queries.