If you want total dissapear in the pocket - the KelTec P32. This little guy is so light but it does just chamber the .32ACP. The Kahr PM9 shoots the 9mm, is light enough, and thin enough, to suggest a serious pocket piece. I have easily pocketed the MK9, although, a bit heavy.
I have the P32 and MK9, but I must get a PM9 in all black one of these days. I think most of the bugs have been worked out, and it really is probably the ideal pocket pistol combining thinness, lightness, and with an effective caliber.