Online Collaboration Tools

How to communicate and share work when working in a group online?

e-mail - that is pretty straight forward, but can get quite cumbersome very fast.

googledocs - the gold standard at the moment - very convenient.  Need to have a google account before you can start, but who does not have a google account these days?

dropbox - a tool you can use that creates similar folders on different computers (even smart phones) - it also keeps on online copy.  Need to download the application before you can start.