I am just loving OnToCalendar right now. It is a free (opensource) application created by SoundsLikeObiwan that gives you a few more menu options in the email application. It simply lets you add a email including the subject as a calendar item or task.
Nikolaus let me know that with version 3.5.9 things just got better. You can now have the application globally add the sender of the email to the calendar item as a meeting invite. They have also added experimental support for setting global reminders and due dates for tasks. I got a Java Null Pointer error while trying that feature out but hopefully the upcoming version 3.6 will fix that.
I will keep you up to date on the updates. You can pick up the latest beta at the links below:
Keep up the good work SoundsLikeObiwan!