You may not have heard of the Hang - it's a relatively new instrument and it's extremely hard to get hold of one. First invented in 2000 by PANArt, they are hand-built in Switzerland by two very dedicated people, Felix and Sabina.

[youtube=http://www.youtube.com/watch?v=3dSlBqsoAa4&w=700]This shows you three stages in the evolution of the Hang -not sure that 'drum' really covers it.

They only make you one if you ask nicely (no emails, fax or snail mail only). If they agree, then you may have to wait up to two years anyway. You have to pay cash, in person, in Bern (Switzerland), and you can only buy one at a time. You can buy them on eBay and so on, but it'll cost at least five grand.

The Hang Drum is played with the hands. Everyone who gets to play one falls in love with it a little bit. It's incredibly sensitive and dynamic - it rings pure and true. It sounds like magic. The entire disc resonates at a central frequency as your hands move around the edge teasing the notes out.

Two Different Drums

There are two types of Hang, the Mk1 and Mk2. The Mk 1 had 8 notes around the Ding. These were available in 45 different tunings, and PANArt produced nearly 4000 of them.
The Mk 2 is basically the same shape but has a brass coating on the top as well as around the rim. The Mk 2 comes in only five different tunings and has only seven notes around the Ding. It is a more sturdy design, stays in tune better over time, has a slightly longer and purer ring and a rounder edge, so the rim doesn't hurt your hands so much.

Listen to these solos:
[youtube=http://www.youtube.com/watch?v=_rXcdcDB2S8&w=700]

If you can't afford a Hang, try a HAPI:
[youtube=http://www.youtube.com/watch?v=PW-GZ05htLE&w=700]

Bear in mind that to get any good at these instruments, you need to smoke a LOT of weed, say no to Heathrow Terminal 5 and eat a lot of mung beans. Joking aside, they make pretty sounds.

Links:
Hangblog
Soniccouture (developed a synthesiser version)
Hangmusic (has a sort of radio station thing)
This explains the scales
And where would we be without Wikipedia's page on the subject?