This is one of those tools that you have to absolutely give a test-drive to feel yourself how cool (and yes, useful& effective) it really is. Groove is a collaboration tool developed by the creator of Lotus Notes, Ray Ozzie.

Give clients a walkthrough of their new site with it, manage your meetings, meet virtually and sketch out your ideas on the sketchboard, collaborate on documents, ... I could go on and on. There are also excellent add-ons that are sold by third-party companies.

The only catch: the price. I might be tempted to buy it and start using it nonetheless, I believe it might be worth the investment.