One of the best tips for card-making (my second true love when it comes to crafting--scrapbooking being the first) I have ever heard come from a scrapbooking television show I watch regularly. (With a cup of cocoa, might I add.)
Take an 8 1/2" by 11" sheet of cardstock, cut it in two evenly, and then score down the middle of each piece. This will yield two 4 1/4' by 5 1/2' pre-made cards which just happen to fit perfectly into the invitation-sized envelopes at your office supply store which just happen to cost $13 for a pack of 100. That's half the cost of what I have been paying to buy mine in bulk at a local scrapbooking store.
This year I made 7 different designs for my Christmas cards. (Only posting one here--love how this turned out!)
I just assembled them on a piece of 4 1/4" by 5 1/2" piece of cardstock and then when I was done, ran each assembly through my xyron and adhered it to my pre-made cards. Easy as can be! Thanks Scrapbook Memories!!