Can I find out the return value before returning while debugging in Visual Studio?
Not that I know of. Note that if you do add a variable, it will get removed by the compiler in release builds anyway...
Update:
This functionality has been added to VS2013.
You can see the return values in the autos windows or use $ReturnValue in the watch/immediate window.
The value can only be seen directly after returning from the function, thus the easiest way to access it is by putting a breakpoint on the function call and step over (F10) the call.
Update for VS2015: boo! unfortunately, it doesn't appear to be in VS2015 (devenv v14)
Update for VS2017: it's back. (devenv v15)
This can be done in Visual Studio 2013 with CLR 4.5.1 according to the customer feedback site. It was not available in previous versions for C#.
(Visual Studio 2008 and earlier supported it for VB.NET. It has always been available to C/C++ developers.)
I agree that this is a very useful thing to have: not only seeing the return value of the method before stepping out of it, but also seeing the return value of methods I just stepped over. I implemented it as part of a commercial extension to Visual Studio called "OzCode".
With it, you can view method return values right on the code editor, as sort of a HUD-display:
For more information, please see this video.