Love this idea of planning your dates with your spouse in advance. That way there is no fuss, no worry, and no need to think. (Photo stolen from From shannonbrown.typepad.com)
In each envelope, you could have movie tickets...
restaurant gift cards...
or concert tickets depending on the activity for that night.
You could even include cash to pay a babysitter.
I wouldn't categorize these date nights by month the way they did. I would do it by type of date. What if I didn't want to go to the movies one month? I wouldn't want to be tied to that activity. Either way, it is a fabulous idea.