TouchDown, one of the oldest (which does not automatically imply best) should also allow this, though their description isn't quite as clear: "Corporate Data Separation: TouchDown keeps your corporate data separate from your personal data. Without TouchDown, your employer can actually flatten your phone to factory defaults. With TouchDown, they can only remove corporate data belonging to them, leaving behind your personal information."
I might have skipped TouchDown at the time, because 1) it does not integrate with the native calendar and contacts (or at least the screenshots imply that it is a built-in functionality), 2) it looks like from Gingerbread era, 3) has separate versions for phone and tablet.
