The most common would probably be C and it's variants, C++ and Objective-C (the latter mostly for Mac programs). In web development, you're more likely to see PHP and Python. In Enterprise software, you're probably going to see Java or C#.
For games, it depends on what engine you're using. The Source engine (used by Valve in all of their games) has you code directly in C++. Unity3D runs on top of .NET so you usually use C#. The Unreal Engine (used in Unreal Tournament, Gears of War, and Bioshock, among others) uses a custom scripting language called UnrealScript.