I received, a while ago, a pack of 30 fine art postcards, and I love them. They are perfect for sending a quick hello. Postcards are cheaper then notecards to send, and people often save post cards on refrigerators. I also find that postcards take less time to put together. People often tell me how much they enjoy a postcard I have sent them out of the blue.
Be sure to check out all the other frugal ideas here!