My friend and I work in the same field as Graphic / Web Designers and have worked on a few projects together. Our biggest challenge is location. He's located at one end of Jamaica and me at the other, so I'm always looking for ways to improve our virtual work relationship.
Over the years we've used several applications to aid us in our collaboration, BaseCamp (free), YouSendIt, Hamachi along with others. Hamachi was the last one we used and it was a lil difficult to get it to work seemlessly between a Windows Vista Laptop and iMac (running OSX 1.5). Plus there was no official interface for mac users ( I had to type commands in the terminal whenever I wanted to use the application). As a result I went looking for an alternative and I found it - DropBox.
Now dropbox was a term I first heard being used at a advertising agency my wife worked at and was only available to macs. Once all the macs are on the same network users could add files into a default shared folder know as a 'dropbox.' But I came across another DropBox that was available for the specific platforms - Window, Linux & Mac (Ahhhhhhhhhhhhh!!!!! As the choirs of angels sing and the beam of light shines done upon my ignorance :-) ).
In no time I had DropBox installed on my mac and my friend and I were able to share files, it was sweeeeeeett!
DropBox initilally gives you 2Gb of storage for free, which you can upgrade if you want. It allows you to see the various versions of a file once changed or updated, restore deleted files, see previes of images and share specific folders with anyone you desire.
The lovely thing about DropBox is that it's linked to a physical folder on your computer, has a web interface to manage your account and shares files over an SSL connection. If you have growl installed on your mac you'll also get a notification everytime I file/folder is updated.
DropBox is a great collaboration tool, you should get it!