TBH i think Gmail is the ultimate in e-mail applications as it was said above its fast due to little graphics and you never have to delete any emails unless yr like sending your self 10mb emails every second. The fact that you can easily search through your emails to find the ones you want is alsoa nice little tool and the fact its GOOGLE. What more can be said - also have invites
Note: Gmail is set to be released soon as the beta testing is pretty much done, and googles IM program is alos out for testing and includes a notification tool for your gmail account. What more do you want
Googles im
www.google.com/talk