A small and steady stream of 4" screen enabled apps are now making their way into the App Store.
Sister site AppShopper.com allows you to see a realtime list of these new iPhone 5 enabled apps using this "iPhone 5" search query. That url shows all recently updated iOS apps that mention "iPhone 5" in their What's New update description. There may be a few false positives, but the majority of apps listed are listing support for the new iPhone.
There are a relatively small number of updates so far, but the list will continue to grow as we approach the iPhone 5 launch on September 21st. Only a handful of games are compatible so far. These include Pangea Software's catalog including Enigmo 2 and Mojang's Minecraft - Pocket Edition.