Dave Battino wrote an article which was a roundup of ultra-compact keyboard and pad MIDI controllers in the December 2013 issue of keyboard. He shared the video he created to show these itty bitty MIDI devices.
David Battino has been plugging things into MIDI jacks since 1985. He's the founding editor of Music & Computers magazine and co-author of The Art of Digital Music, which Music Tech magazine (UK) called a "jolly good value." He has covered music technology for Electronic Musician, MacAddict, Make, Maximum PC, and Revolution, and currently writes Keyboard's "Key Secrets" column. More at www.batmosphere.com.