Korg, maker of miniature synthesizers such as the Monotron and Monotribe, have two more analog pocket-synths for me to noodle around with for 20 minutes then put in a drawer: the Monotron Duo and Monotron Delay.
The Delay (above) is great for spacey 1970s-style explorations, while the Duo (below) has two oscillators. Play both videos simultaneously, if you dare.
Product page [Korg]