One of the members of the Finger Lakes Flute Circle asked me an excellent question through our Meetup website, "What key are most of the flutes?"
The key we use the vast majority of the time at the Finger Lakes Flute Circle is a mid A minor. By everyone having a flute in the same key, we are readily able to play along with each other. The mid A minor and G minor are the most popularly purchased keys from makers; pretty much everyone that's a fan of Native American flutes will have an A. The mid A minor well accommodates the finger flexibility of most beginners and the finger hole reach for most sizes of hands. The beginner flutes that we have available for use, Northern Spirit flutes in A minor, are economical, durable, and sound very nice!
That being said, you can get Native American flutes in all kinds of keys, mid range, high, bass, and sub-bass (note that there is not a standardized terminology for pitch ranges)! The next most popular key might be the mid F# minor, which is thought to be close to many "grandfather tuned" body measurement proportioned traditionally constructed flutes. Many folks love the grounding, soothing tones of the bass and sub-bass flutes. The lower the flute, however, the more challenging to reach to wider spaced finger holes, and the greater the demands on breath control.
Some people develop the terrible affliction of flute collecting. There are so many special flutes, different keys, different woods, different makers. For some, it's a malady for whom there is no cure, except for exhaustion of funds or the wrath of one's spouse.
Here is a link to an astounding flute key reference on the fabulous www.flutopedia.com by Clint Goss (I count sound samples in thirty keys): http://www.flutopedia.com/keys.htm