If you want even smaller, the Olympus T20 is just that.

It has a GN of 20 (meters) with ISO 100.

Its shoe makes it a little uncomfortable in a shirt pocket, but otherwise it is the right size.

An info link: http://www.star.ucl.ac.uk/~rwesson/esif/om-sif/flashphotogroup/t20.htm

And an eBay listing: http://www.ebay.ca/itm/OLYMPUS-ELECT...item2eac8cf933

If you decide to try to get one, be sure that the battery door is intact, and that it comes with the sliding panel at the back. That panel reverses. One (almost blank) side is used with TTl flash on a number of OM bodies, while the other is used to either set the in-flash auto range or to indicate the aperture to use for different distances.

The back panel comes in two different versions - if you need feet, don't buy the one that only shows distances in meters.

I think I have three of these - they fit in just about any camera bag.