And now, at 50 0ff until July 12!
I have heard OvernightPrints.com to be recommended by some in the crafting community.
You can use their designs or upload your own.
Postcards are a great way to showcase your busienss - hand out as business cards, send to customers with a discount code, place on counters at beauty shops, etc.... overnightprints.com - postcard sale: http://bit.ly/r1yPZ
Here is a great article about using postcards for business:http://www.handmadenews.org/article/index.php?id=1903