My current company is pretty small, so I just put any specified dates on my Outlook. At my previous company, we just would have Word calendar print-outs and "pencil in" dates on that. That way I could take it around or just pin it up at my desk and programs managers could see what all was going on.
I have always been in companies where the person who is executing the emails is the calendar keeper. The big thing in my opinion is to only have ONE PERSON keep the calendar or it will become chaotic!
PS - Marketo is supposed to be releasing an email calendar later this year!!