A very serviceable tuckable holster you don't have to wait for - Galco SkyOps Ambidextrous Holster Fits Glock 19

Custom holster makers are the way to go (Milt Sparks, TT Gunleather, etc.) if you want the absolute best available in tuck-able gun concealment, but you will have to wait months for them to be able to get to your order. While you're waiting, the Skyops holster is a well made, thin, comfortable option that occasionally needs readjusting, due to its single hanging point on your belt, and the somewhat flexible hanger that can allow the rig to move out of its optimal degree of cant.
That small quibble aside, though, I'm a fairly trim build and can successfully conceal a Glock 19 or full sized 1911 with a tucked in polo shirt, and very comfortably so if I put the gun in the small-of-back position.
So, a great concealment option that's slightly flawed, but available immediately from several venders---though of course, why do they matter when there's Optics Planet? ;)

Pros: Price, concealability
Cons: Only one attachment point can allow gun to shift quite a bit if the belt isn't tight.

This review was written in the old system and had content requirements that are different than reviews written today.