Lots of cool options there!

REMEMBER TO ADD AN RSVP BY DATE!  If you don't you'll be scrambling to call your friends and family so that you can get their RSVPs (granted, you might be doing that anyways)

By adding a date, there's a bigger sense or urgency, and you're more likely to get fast replies.  

Also consider having them RSVP online, instead of using a Reply card.