Make Visual Studio to add .dll to GAC after each build

Go to Project > Properties and enter the following into the Post-build event command line:
(on Windows Server 2012)
"C:\Program Files (x86)\Microsoft SDKs\Windows\v8.0A\bin\NETFX 4.0 Tools\gacutil.exe" /i
"$(TargetPath)" /f
(on Windows Server 2008)
"C:\Program Files (x86)\Microsoft SDKs\Windows\v7.0A\bin\gacutil.exe" /i "$(TargetPath)" /f

Remember to:

• run Visual Studio as Administrator
• sign the assembly