All of Doomfist's skins are now on the Overwatch PTR, and you can see them here.
There are 10 skins in total, and when you add in the rest of his customization options, like sprays, emotes, voice lines, and the like, Doomfist has 57 customization options. You can see all his skins below.
The Rare skins come first, with nature themes. They are Daisy, Lake, Plains, and Sunset. They'll cost 75 Credits each. The Epic skins (250 Credits each) come next, and are named Cheetah and Painted. Lastly, the four Legendary skins (1,000 Credits each) are Caution, Irin, Avatar, and Spirit.
If you want to dive into the PTR yourself, you can find the details on how to do it over on the Overwatch blog.