Product review (5 stars): Clarinet Saver
Using this in my office in a cabinet that holds my clarinets. The building I work in is horribly dry and I've lost a couple of instruments and had cracks in others because of these conditions. I can't humidify my office enough to make a difference, but storing the clarinets in a humidity controlled cabinet will help to make them less likely to crack.

I've been using this for about two weeks and it works well. It seems to hold water for a long time, the fan is not that loud, and the gauge is fairly accurate. I love the thin tape electrical cord - it makes it easy to run into the cabinet. I wish it wouldn't default back to such a high humidity level when I first turn it on, because it's a pain to move it from the ~70 to ~50% range each time. However, it is designed for cigar owners and not clarinet owners.

Don't get anything less than this if you are planning to store wooden instruments in a humidity controlled cabinet. A larger humidifier would overwhelm the space, and passive humidifiers such as bowls of water and case humidifiers don't work at all. It may seem pricey, but the cost is actually quite cheap considering what you lose if you crack a wooden instrument.