1. Email, no other online free email can beat Gmail.
a. 25GB storage, and free
b. Label : it is better than folder, more like Tag. so you can have multi-Tag/label, easy to manage your email
c. mobile access : GPhone is the best, iPhone supports Gmail well
d. integrate well with google calendar, and google doc.
2. Calendar, well designed, convenient to use.
3. Google Doc. agent needs share a good number of documentation with clients. Google doc is good way to do that. you also can label the doc. for easy manage.