I would love to have a 3" bbl K-frame full underlug 38 Special (not a 357). That would be one of my dream revolvers. The underlug not so much for looks, but to reduce muzzle flip. I tend to like front-heavy revolvers. (I know the OP stated 4"; but 3" is my preference. Otherwise, I think we're on the same wavelength.)
testuser79: No, the model 66 doesn't cut it - it's not a true underlug, and it's a 357 (I want a 38). Yes, the model 66 is a fine gun. But it's not what I (and the OP) described as above.
buck460XVR: Yes, the 686+ w/ 3" bbl is very close. In fact, I have one. It's my carry revolver. I love it. But it's an L-frame; not a K-frame. So it's not what I (and the OP) described as above.