Guardians of the Galaxy steals some of its visual style from the paintings of Rene Magrite and pulpy sci-fi features from the 50's and 60's. That opulent style is also a theme that echoes in some of the early concept art for the film done by Jared Marantz and Anthony Francisco. Marantz was responsible for most of the 2D and 3D character design for the Badoon and side characters such as the Rhino Man. Francisco did the concept designs for Groot, the Sakaraan Soldiers, Korath, The Collector and Karina.
To see more of Francisco's other concept designs go to http://www.ubermonsters.com.
For Marantz, you can see his other designs at
Jared Marantz designs:
Anthony Francisco designs: