I like that "Ghost ring sight" Dave Sample posted, it looks intriguing.
Some years ago I damaged the rear sight on a pistol and a gunsmith had a replacement with a narrow notch. I asked if he could widen it and he did using an "inverted V" pattern. With the green dot sight paint on the front sight it was incredibly fast to pick up the alignment. I think someone made one commercially that was similar to this, but I don't recall the name.
Here's a crude illustration of the sight picture.
The narrow top allows for precise vertical alignment and the wide angle allows you to quickly see if the sight is left/right of center. Ever seen a sight like this one?
BillCA in CA (Unfortunately)