Just picked one of these up for $25 at my local GC.

http://www.guitarcenter.com/Akai-Professional-SynthStation25-Piano-Keyboard-for-iPhone-and-iTouch-106217805-i1513163.gc

Though it's billed as being for iPhone/iTouch, it actually works as a class compliant USB midi controller (but you need an unincluded USB cable with the more unusual mini USB connector) and is bus powered.

It has mini keys and only 25 of them, both of which really annoy me, but I bought it to use with my laptop and it's small and only cost $25, so...


The keyboard has a reasonable feel for this type of thing - much better than some other mini kb's which I have found to be almost unplayable. It is velocity sensitive and feels relatively solid.

The pitch and mod wheels have a surprisingly nice feel and are very usable.

The 8 buttons all send midi CC's, though they are hard coded as follows:
Prev     85
Next     84
Down     87
Up     86
Drums     83
Synth1     80
Synth2     81
Synth3     82

But note that the Up and Down buttons also transpose the kb up and down so they aren't very useful for midi.