They are from left to right (or top to bottom) Sally Hansen Hidden Treasure, Nubar 2010, Nfu-Oh 38 and GOSH Rainbow. As always, photos can be clicked for a larger image.
My conclusions - they are alike. So much alike that I suggest you pick one you can easily get your hands on and call it a day. Unless you are like me and like the hunt. I will say that the formula on the Nubar is better. It's thinner and you can put a few coats on without it building up and looking thick.