Being a long-time Visual Studio user, I’m extremely comfortable with VS themes, especially the dark theme that’s been present in both VS2012 and VS2013. I was dissatisfied with the theme choices in the Unity-bundled version of MonoDevelop and decided to make my own version of the VS2013 dark theme. It won’t look the same in every way, as Visual Studio had a lot more color choices than MonoDevelop, but it should be familiar enough that Visual Studio users will feel comfortable.
The theme is available at the GitHub repository. To install it, just follow the instructions on the repo’s main page.