Google Apps for Business starts at $5/user/mo. and offers email, Google Drive/Docs (30GB of free space, expandable up to 16TB), Google Calendar, etc. It's been a great solution for my small business, mainly because it allows us to collaborate on Word documents either locally in Word or over the Web in Google Docs.

I'm surprised no one else has suggested Dropbox, although it doesn't include online collaboration tools and is much pricier than Google. IMO it's definitely the best file-syncing tool.