I recently came home with about a thousand greeting cards we are not allowed to sell at the store... Long Story! They all have very funny colorful photos on the front. So I grabbed 2 dozen and cut them to keep only the front flap.
I stuck them in my printer and Voila! Instant totally quirky birthday party invites for Dumpling's 5th Birthday. The best part is that each kid is going to get their own different one!
You could do this with the cards you collect/receive every year. It could be very funny to invite someone with a Santa picture or a 60th birthday card (for a kid's party!)