By far the most commonly used IDE is Visual Studio. This is true for both game development and software development in general.
Some platforms will necessitate using other IDEs. For example, iPhone development requires using XCode, Android developers primarily use Eclipse, Wii development is done in Codewarrior, developing for Linux systems might mean Code::Blocks or KDevelop.
You should try to be comfortable using a range of IDEs, but Visual Studio is the most commonly used IDE in commercial development by far, and it is the one you really need to know how to use efficiently.