Simply put a melodica is a mini keyboard with a mouthpiece that you blow in to make the sound. Great for anyone who already plays piano.

The Otamatone is like no other instrument we've ever seen - and I don't think seeing an instrument in action for the first time has ever made me smile so much. Seriously, take a look at these videos. As you can see in the video you play the notes with one hand on the stem and then squeeze the head to make the mouth sing them. Amazing.

The Otamatone comes in a number of colors and a standard and deluxe version (bigger, louder, and has an audio out).

Ukuleles have become incredibly popular in the last few years due to being easy to learn and really fun to play. Uke's are easy to pick up even for people who haven't played stringed instruments before, and are perfect for that group sing-along with your friends.

This example is an excellent quality starters Uke, with a kit including everything you need to get going.

The Theremin is an early electronic musical instrument controlled without physical contact by the thereminist (performer). It is played my moving your hands close to the antennae to control the pitch and volume, to create strange, eerie, sci-fi-esque sounds. See this video for one in action.

This example is a more affordable version with just the pitch control. There is a more traditional two control theremin here.