I have a 637 jframe, great gun. You could always go with a .357 jframe and then you still have the option to shoot .38. Not really a pocket gun though, at least with the jeans I wear, looks like I have a sandwhich in my pocket. Works good in ankle or IWB holster. Also nice for the car.
I also have a P3At and it is truly a pocket gun, fits in the great or easily in a ankle holster. My dad has a Ruger LCP, pretty much the same gun but add 50 bucks to the price. I think Kel-tec has built a nice little reputation plus a great service center. I would be a little worrie about a ruger lcp shooting me in the leg when I drop it (heh like the SR9). All great guns though, but for a true pocket gun, I would go with the P3AT for sure.