I emailed a research chemical company and got back a link to temp.pm. Checked it out and thought, "Huh, that's pretty bad ass." So, off I went looking for other similar services and found sms4tor. Here's the onion link:
Seems legit. I'm not suggesting that PGP should take a backseat where the most sensitive data is concerned, but I do like the idea that the message is deleted once it's viewed. This one doesn't let you place an expiration on unread messages like temp.pm, however. If anyone wants to quiz the developer, I'm pretty sure they are redditor /u/sms4tor. Stay thirsty my friends.
Thanks!