Go with the Glock 30. The Sig P220 is a fine firearm, but too big for concealed carry for most people if you ask me. And I cannot scientifically describe why, but the Glock 30 is the most accurate Glock I have ever owned (I've had two glock 27s, a glock 23, glock 19, two glock 17s, glock 34, glock 35, a glock 21, and two glock 30s). I no longer have any of them, unfortunately (the glock 21 and a glock 17 due to theft and the rest I sold because I am a gun slut).
The Glock 30 is stout enough I get such a positive grip its amazing, the thick walls of the grip fit my hands perfectly, and the short slide is weighted perfectly to make muzzle flip almost nonexistant. I can outshoot any of the other glocks, including the full sized glock 21, with a glock 30. They conceal very well, despite their stockiness, and are reliable as sin.
The rugers and 1911s mentioned are great, but many are too big for concealed carry compared to the 30. If the Glock 30 is too wide for you, my personal preference would be a commander-sized 1911. Any 1911, though, is so thin they conceal well. But I honestly think you'll be happy with a Glock 30.
I carry a Kimber 1911 Gold Match now, but I wouldn't mind having something I can abuse and carry comfortably when grocery shopping... another Glock 30 for ol' Murdock, perhaps?
I had two Glock 30s and my heart flutters just remembering them... I want another one, now. Thanks, ya bastard!
TRL