Quick link: Google Apps, Free version
I rather like Google Apps. Especially Google Mail and Google Docs can be of great use to small teams and could really be all you need. Unfortunately, though understandably (they are a business, after all), Google have been limiting the free offering a bit. Whereas it used to be free for 50 users, you now get at most 10 before you have to switch to a paid plan, like Google Apps for Business.
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