I have been checking my local Sally's every week to get the China Glaze Crackle nail polish. Apparently they sold out of it in the first week they had it in stock. Finally I got my hands on three of them and here are the swatches:
The trick with these polishes is to apply thin coats. When you do thick coats there isn't as much cracking in end result. Also, the base nail polish needs to be completely dry before you put on the crackle.
OPI and Sally Hansen also sell crackle nail polish but they are much more expensive, so if you can get China Glaze I would get that instead.
Here is a video I made showing a demonstration of the nail polishes: