Update: This add-in breaks with the new Monodevelop 4 that ships with Unity 4.3. However, Monodevelop 4 comes with a “duplicate line” function for which you can assign a shortcut in the key bindings in preferences.
This is one of those things that you don’t know you need until you have it, and the one feature I’ve missed the most since my Eclipse/FlashBuilder days:
I wrote a little MonoDevelop Add-In that lets you duplicate the line you’re on (or multiple selected lines) by pressing Alt+Ctrl+Up to duplicate above or Alt+Ctrl+Down to duplicate below your current position. In combination with Alt+Up and Alt+Down (which move selected lines around), this comes in super handy for dealing with repetitive blocks of code (such as variable declarations).
You can download the plug-in here: http://www.philippseifried.com/files/MonoDevDuplicateSelection.zip
To install, close MonoDevelop and copy the DLL into the folder /Applications/Unity/MonoDevelop.app/Contents/MacOS/lib/monodevelop/AddIns on Mac, or [Unity install path]/Unity/MonoDevelop/AddIns on Windows. After starting MonoDevelop again, you can use the keyboard shortcuts, or access the functionality from the Edit menu.
Note that you will need to re-install the Add-In if you update Unity!
The Add-In is under MIT license, so feel free to use and redistribute it as you see fit. I’ve tested it on Windows and Mac (where I’ve been using it daily for a few weeks), but of course standard disclaimers apply: Use at your own risk!
Shameless PlugCheck out my upcoming 80s-cartoon-themed space opera "Ace Ferrara And The Dino Menace"!