Microsoft Exchange Online
For all the attention directed at Google Apps, Microsoft has been steadily improving its Office 365 offerings. If you don't care about editing online documents, the stripped-down Exchange Online Plan 1 delivers compelling value at just $4 per user, per month with 50GB of mailbox storage. Aside from email, Exchange offers Calendar, Contacts, Notes and Tasks to help get a leg up on productivity. All features can be accessed from a wide variety of devices, including all mobile platforms, online, or from the Outlook desktop app, which is available on both the PC and the Mac.