Think outside the envelope -- not all save-the-dates need one. Case in point: this poster-like message that is off the charts when it comes to cool. 

Print your note on an oversize printout of a vintage map you've scanned and tinted (or use Cavallini & Co.'s map-inspired wrapping paper). Fold to card size, with blank side out, then stamp and address and seal with a sticker. 

Save the Date Sticker 1
Save the Date Sticker 2
Save the Date Sticker 3

Resources
1 1/4-inch round labels, Paper Source. Calligraphy, Deborah Delaney, 212-877-8773.