Well here's a wedding card I made with a stolen pattern -- adapted a little to be fun, but classy.
It's a basic pocket card - a decorative sleeve that matches the actual "card" (the tag) that tucks inside it:
The tag itself can be any color, with any content you like. I used a sewing machine to do up the edges and seal the pocket. I also used a rub-on transfer for the simple 'celebrate love' greeting.
Shown separated you can see the two pieces a little more clearly. This could easily be used for any holiday or celebration -- a 'new address' announcement, baby announcement (include a little picture on the tag?), a birthday card, a party invite, a gift card holder -- be creative!