I am having fun discovering this iconic synth from the 70s, although in virtual form. (Rumours though say Behringer is building a cheap hardware clone).
The Arp2600 was most noticeably used by famous musicians such as The Who, Steve Wonder, Herbie Hancock and many more.
More importantly though, Ben Burtt used it to create most of his iconic droid sounds in the original Star Wars trilogy, including RD2D.
Here are some more technical info on this synth http://www.vintagesynth.com/arp/arp.php
I made these example sounds while learning the instrument. Next step is to recreate the sound of R2D2.