Unity3D: Reduce compile time with Standard Assets
While there are many ways of reducing compile time in Unity, like moving your code in DLLs, I recently stumbled upon a very simple way that most developers can do, right now, and immediately get results: Create a folder named "Standard Assets" and move parts of your code that don't change that often (like plugins, core code, etc) in it. According to Unity's documentation (emphasis mine):
Scripts that are placed in the first group ("Standard Assets", "Pro Standard Assets" or "Plugins"), will take longer to compile, since when they are compiled the third group needs to be recompiled too. Thus if you want to reduce compile times, put scripts that seldom change into group 1 and scripts that change a lot into group 3.
This is, I think, from Unity 4.1.2 documentation, but I have timed the compile time before and after moving my scripts to Standard Assets in Unity 4.3.4f1 and found that it has indeed reduced the compile time to half; from ~9 seconds to ~4.5 (for a project with more than 1,500 C# files).