Thanks to a hot tip from Goodnight Little Spoon, I just found out about the very groovy-looking Penpal Party. It is billed as "a letter-writing exchange... for stationery and letter-writing enthusiasts."
NO, I'm not going to join - I have too many other letters of me own that need responses, and I'm very happy with all the letters I write and receive.
But for those of you who are looking for a few more pen pals, or anyone who will write back, really, it looks like a great idea and a great place to start.
The gal who founded it is a designer, and her designs are reeeeeeeeally cute. You can see 'em here, but of course she did the way cute design on Penpal Party, too.
You can even see some fun Penpal Party photos here, too.
If you decide to sign up, let me know how it goes!
UPDATE: This project has been discontinued. You can read the full comments for info.