LaunchBox - LaunchBox is a portable, box-art-based games database and launcher for DOSBox, emulators, arcade cabinets, and PC Games. Download it free!
GOG.com - DRM-free game store, selling both new and old titles. No clients required.
GameEx - GameEx is considered to be the most powerful and feature rich front-end for MAME, GameBase, Daphne, PC Games and all command line based game emulators, along with being a complete Home Theatre PC solution.
Origin - Origin is your new digital playground. It’s where you go to find the best that EA has to offer.
GamersGate - Buy and download games instantly for PC and Mac.
Epic Games - Computer game storefront that gives 88% of revenue to developers