Is there any way to make Visual Studio stop indenting namespaces?

Here is a macro that could help you. It will remove indentation if it detects that you are currently creating a namespace. It is not perfect but seems to work so far.

Public Sub aftekeypress(ByVal key As String, ByVal sel As TextSelection, ByVal completion As Boolean) _
        Handles TextDocumentKeyPressEvents.AfterKeyPress
    If (Not completion And key = vbCr) Then
        'Only perform this if we are using smart indent
        If DTE.Properties("TextEditor", "C/C++").Item("IndentStyle").Value = 2 Then
            Dim textDocument As TextDocument = DTE.ActiveDocument.Object("TextDocument")
            Dim startPoint As EditPoint = sel.ActivePoint.CreateEditPoint()
            Dim matchPoint As EditPoint = sel.ActivePoint.CreateEditPoint()
            Dim findOptions As Integer = vsFindOptions.vsFindOptionsMatchCase + vsFindOptions.vsFindOptionsMatchWholeWord + vsFindOptions.vsFindOptionsBackwards
            If startPoint.FindPattern("namespace", findOptions, matchPoint) Then
                Dim lines = matchPoint.GetLines(matchPoint.Line, sel.ActivePoint.Line)
                ' Make sure we are still in the namespace {} but nothing has been typed
                If System.Text.RegularExpressions.Regex.IsMatch(lines, "^[\s]*(namespace[\s\w]+)?[\s\{]+$") Then
                    sel.Unindent()
                End If
            End If
        End If
    End If
End Sub

Since it is running all the time, you need to make sure you are installing the macro inside in your EnvironmentEvents project item inside MyMacros. You can only access this module in the Macro Explorer (Tools->Macros->Macro Explorer).

One note, it does not currently support "packed" namespaces such as

namespace A { namespace B {
...
}
}

---

EDIT

To support "packed" namespaces such as the example above and/or support comments after the namespace, such as namespace A { /* Example */, you can try to use the following line instead:

 If System.Text.RegularExpressions.Regex.IsMatch(lines, "^[\s]*(namespace.+)?[\s\{]+$") Then

I haven't had the chance to test it a lot yet, but it seems to be working.

As KindDragon points out, Visual Studio 2013 Update 2 has an option to stop indenting.

You can uncheck TOOLS -> Options -> Text Editor -> C/C++ -> Formatting -> Indentation -> Indent namespace contents.

Just don't insert anything before the first line of code. You could try the following approach to insert a null line of code (it seems to work in VS2005):

namespace foo
{; // !<---
void Test();
}

This seems to suppress the indentation, but compilers may issue warnings and code reviewers/maintainers may be surprised! (And quite rightly, in the usual case!)

Probably not what you wanted to hear, but a lot of people work around this by using macros:

#define BEGIN_NAMESPACE(x) namespace x {
#define END_NAMESPACE }

Sounds dumb, but you'd be surprised how many system headers use this. (glibc's stl implentation, for instance, has _GLIBCXX_BEGIN_NAMESPACE() for this.)

I actually prefer this way, because I always tend to cringe when I see un-indented lines following a {. That's just me though.