Matt Wisniewski is a web developer and self-taught artist based out of Brooklyn, NY. He has been using Photoshop since he was a child, and he loves to create visual experiments through collage. His art usually begins with a portrait, and he quickly combines textures until something catches his eye. If you want to learn more about his work, check out this great interview on Yatzer.
If you like double exposure photography, you'll be sure to love these double exposure paintings by Pakayla Biehn. Biehn collaborates with multiple photographers to create these masterful re-creations. At first glance you might mistake them for photos. Her attention to details is amazing. For more, check the Double Exposure series on her site.
Liesl Pfeffer is a photo-media artist from Melbourne Australia. She has some very cool patchwork photo collages. I love the sharp deliberate use of straight edges used to represent the mountains and also the use of cut out photos of the sky and grass to help create the collages. You can find her on Blogger, Flickr, Twitter and Tumblr.