I'm guessing this depends on the OS, among other things.
I would guess that development for Windows using DirectX would "force" people to use Visual Studio, but is that always the case? What about when OpenGL is the graphics API?
How about Java? Is Eclipse the norm?
UPDATED:
I guess the general consensus is that there aren't really specific IDE's for game development. It just depends on what language you're working with.
Certainly C# and XNA require Visual Studio (or C# Express Edition).
C++ can be developed on any platform; anything from vi/emacs (or any text editor) and the console on Linux, or Visual Studio handles C++ quite nicely on Windows systems, and then other IDEs such as Code::Blocks and Dev-Cpp are also commonly used on multiple platforms. There are a couple IDEs for Linux, one of which is KDevelop, and those are also used.
For Java, Eclipse and NetBeans are the top IDEs, but again it can be written in any text editor and compiled via the command-line app "javac".
DirectX and OpenGL do not dictate the IDE, they are just graphics layers on top of the language of your choice. Of course, DirectX basically needs Windows unless you're crazy enough to try testing in WINE or a virtual machine, but OpenGL can be developed wherever you want.
I personally develop in Java on Ubuntu Linux, and Eclipse is my favorite IDE by far. On Windows, I love Visual Studio for C++ and C#/XNA.
What you're doing with the language (game development) has nothing to do with the IDE you're using. If you're on Windows (sounds like it), the most common IDE for C++ is Visual Studio. If you're using C#, the most common and powerful choice is Visual Studio, especially when coupled with Resharper. The addons and features of VS 2008 make it a worthwhile investment.
There is also the free, lesser featured version of VS, Visual Studio Express. Some other free editors as pointed out by the comments here are MonoDevelop and SharpDevelop.
The Java community have 3 main editors. NetBeans and Eclipse are the most popular and are free. IntelliJ IDEA is another big one, but it costs money. However, it has some really cool features, something like a built-in Resharper but for Java (it is made by the same people, after all).
Typically, in my experience (which is working in the games industry for over a decade, and at a number of different companies), most studios use Visual Studio as the IDE no matter what platform. We're doing development for DS, PS3, 360, PC and other platforms at my current place, but everybody uses Visual Studio (with makefile projects for non-Microsoft platforms) for actually editing code. Of course you can't use VC to debug other platforms, so you'll have to use whatever the hardware vendor supports for that.
I'm only really talking about larger game studios here, though (I mostly do console development). I've no real experience of what people use for, say, Flash or mobile phone games or that kind of thing.
I worked a bit in game dev. Most of the games were in flash so we used FlashDevelop and Flash.
As for the DS team, they used Visual Studio if I'm correct.
For classic C++ game development, it is Visual Studio and the Wholetomato Visual Assist X addon which massively improves Intellisense and refactoring support when working with C++ source code.
As for Java, yes, it is Eclipse and sometimes Netbeans.
Visual Studio, whether it's being used as the native platform for Windows and Xbox, with SN Systems ProDG for Playstation platforms or makefile projects for something else. And we avoid Codewarrior like the plague if we can help it.