www.lcipaper.com (I didn't use this one because I decided not to make my own, but it was very intriguing when I was toying with the idea)
www.mygatsby.com This site has more "print your own" style. I ordered some (my in-laws asked if I'd mind making the RD invite, which I LOVED doing! ).
This is how they came out
They also have invites that are more formal, like wedding invites. I had a great experience with them- fast shipping, good product.