I recently came across Aaron Nace's work on 500px and am impressed with his work. Aaron produces digital art that is convincing, using similar techniques to my own, in Photoshop. His work is excellent, he has an eye for light which is key to this process and success of a composite image. A lot of the time we need to hand draw in shadows or recreate highlights to convincingly blend images into a image and make them feel connected to the scene. In fact getting the colour and lighting right is probably more important than how good your selects and masks are. The best thing about Aaron is his generosity, he makes time every day to film a 10-20 minute video podcast on Photoshop or photography in general and doesn't hold back from sharing tips, techniques and inspiration on how he produces his work for free. It is well worth subscribing to Phlearn if you are interested in working this way in Photoshop. If that isn't enough he has created 1-2 hour long tutorials for most of his key work, including the source files. These tutorials are available for $19 but considering the knowledge contained is extremely good value.
Note: Phlearn happens to be one year old today. At the time of writing, Aaron is offering 50% off all his paid for content as well as bundles of 5 for $39, I have just purchased a whole load and have already learnt several shortcuts or better approaches to my own Photoshop skills
Aaron has created some fantastic images both commercially and as part of his personal projects and he is well worth checking out.