I created http://simplepostal.com a year and a half ago. Just never knew how to get it on top of hacker news :)
It's a dumb exception, but you guys might find it mildly amusing.
It lets you send letters, postcards, checks and faxes
Wound up having a decent number of users at some point, but then people started abusing the check sending features. We took it down and built some anti-fraud stuff, but never did anything to acquire users again. It does continue to work perfectly well though.
It's interesting that so many products like these exist in spaces that will probably never be huge and so there's no major VC funded player that may kill them all.
>All included at one low price - printing, postage and shipping. Only pay for what you send. Higher discounts at higher volume. As low as $1.50 per mail.