Advance computer rendered imagery have become sort of a double-edge sword for us designers. On the one hand it enables visual comps with unparalleled realism. On the other hand the technical mastery of such imagery is a challenge - that is until you throw in the advent of high dynamic range lighting provided you can find good sources. Bunkspeed just launched a ginaormous library of royalty free HDRI images for all your rendering needs. Sign up, buy some credits, download, and watch your creative work take a giant step forward.
Resources: Bunkspeed HDRI Library