Nudgemail Free Public Beta
When you get an e-mail that you need to do something about, but just don't need to deal with quite yet, Nudgemail acts like a snooze button to pop that message back into your inbox at the appropriate time. Once you've signed up at nudgemail.com, you can forward messages to email@example.com to put them off for another day (or week, or month). It works with Google Calendar, too.
As of this writing, Nudgemail is in free public beta. The vendor's Web site states that Nudgemail will always maintain a free version, although a paid subscription would include more features.
Note: This link takes you to the vendor's site, where you must sign up to use this Web-based software.