The best handgun ghost ring BY FAR is the Goshen Hexsite:
http://www.goshen-hexsite.com/index2.htm
The Glock version could, with some work, be adapted fairly well to a lot of other guns. Not mine though, just too far off...so...with Tim's permission I've been developing my personally owned semi-clone and while it's beyond funky in the looks dept. and needs custom holsters, damned if it doesn't work extremely well:
This is a target-focus setup - the sights work despite both front and rear being blurry. It feels like it lines up automagically behind your eye, wherever you look. Read the most detailed review so far for more details:
http://www.goshen-hexsite.com/pdf/Handguns_2008June.pdf
Despite being all-black front and rear, it still works as long as there's enough light to ID the target. By keeping the sights dead black they are always darker than the target and your "subconscious" can still use them. You have to practice sighting with them in the dark before you'll believe they work but once you do, it's just beyond cool. And with a target-focus setup, keeping both eyes open is easy. It feels like a red dot sight except there's no actual red dot - and there's also no batteries, wires or glass.