Loveland, Colorado postmarks Valentines with a cachet every year. You can order them online. I have always been in Loveland during Valentines Day (but not this year). All you have to do if you are in the area is to drop your Valentines in the designated mailbox. They stamp the outside and mail it off for you.
The first picture is one of my postcards of Loveland, Colorado.
The second and third are the 2009 Valentine cards you can order. Website is:http://withlovefromloveland.com/