China Glaze just came out with their "Crackle" collection a couple of weeks ago. They have a bunch of different colors ranging from black to a turquoise blue. I picked up the color "Black Mesh" (just a simple black), because that was the only color I was actually interested in.
You have to first put on a "base" color before you add a layer of the crackle polish, so I put on Essie's "My Private Cabana" and let that dry completely before I added the Crackle polish. It takes 3 to 5 minutes for the polish to get the full crackle effect, and it's super cool to watch. I wouldn't say that I would wear this all the time, because it's not normally something I would go for, but it's still pretty cool.
I got mine at Ulta for $7.99 (still a little cheaper than O.P.I.'s Katy Perry "Shatter" polish which is basically the same thing). It's a little bit more than the regular China Glaze nail polishes, but it's worth it.