tiny synth module

[Anya <anyato@xxxxxxx>]

Apologies for hardware question 
(if hw doesn't interest you, please delete). 

I'm looking for an extremely simple, light, and small synth=
 module.  Basically, I'm looking for the lightest and smallest=
 device you can attach to a single keyboard controller or other=
 MIDI controller to produce some audible sound or sounds=
 (ideally, including a sound that approximates piano) out of one=
 stereo headphone jack.

The closest thing I've found is a high-quality Yamaha unit that's=
 probably 18 or 20 ounces with batteries. I really don't care=
 about the quality of the sounds, so if anyone knows of anything=
 even smaller/lighter, I'd really appreciate hearing about it.

Thanks, 
Anya