I recently bought a lap harp and was having trouble tuning it. I downloaded a free app for my iPod called PanoTuner.
Out of curiosity I tried the app with my G Blues Harp. Turns out it's a pretty good tool for learning to bend and overblow, as you can see the frequency change as you play the note. And when it comes to bending I need all the help I can get.

I use an app called "DaTuner Lite" (it's free, too). It displayes a variety of information, including the note one is hitting, the decibel level, the hertz level, plus what octave the note is in (as in G4, C5, Bb4, A6 etc.) It's a very good tool for learning to bend and overblow. Helps to see exactly what note is being hit.

Hmmmm... just out of curiosity, can anyone see my post above this one that I made several weeks ago? I'm told it's there but I can't see it (along with a few other members who also can't see it). Guess I'll give it another go...

I use an app called "DaTuner Lite". It's free and very helpful for practicing not only "straight notes" (simple blow or draw), but bends and overblows, too. It indicates what frequency (in hertz) one is playing at (such as A4 440 hz), plus any cents off either way (up to +/- 50 cents) as well as the decibel level. It responds rapidly and accurately to the notes being played.

So far I've been quite happy with it.