Recorder Plus (free), I've got Pro ($4.99) from iTune Ap Store. Also enhances the built-in video recorder with high quality sound (as good as your mic).
I have an Audio-Technica Pro 35 clip-on mic. When it's clipped on the treble side, it loses the bass. I clipped it on a camera tripod and placed it about a foot-and a half in front of the accordion and it picks up both sides.
It has a 2-in-1 jack that receives an XLR or a 1/4" input, switch for guitar or mike input, with option to supply phantom power, plus a headphone jack for playback.