AG, one of the big reasons I joined this site was to learn more about these parts. I've done all my work in custom integrated circuits, so there wasn't any need for me to know about about these commercial parts. Thanks for pointing this out.
You can also make a very simple relaxation oscillation using an SCR. **broken link removed**
An SCR and PUT are really the same thing anyway, the PUT is just negative and the SCR is positive.