A crucial part of the solution set that I recommend to my clients is Google Apps. For those who have no idea what Google Apps is, please let me explain. Google Apps provides email, calendaring, chat, web site hosting and document services. These services are all online and allow for interactivity via the ability to share all of the services with whomever you want. Of course you are also able to limit access in many of the same ways that you can with a server sites in your office.