Just a little hint for new Unity users on the PC platform. The SciTe/Scintilla editor that comes with the PC version is probably a lot better than the smultron editor that comes for the Mac version. Still it's a complete different level if you use Visual Studio.
Visual C# Express 2008 is a free development environment and it's very good. Besides standards like Syntax-Highlighting it has good refactoring tools and a pretty good intellisense (intelligent auto-completion).
In order to use Visual C# Express, you need to add references to the Unity DLLs inside a new project. On the PC you can grab them from the installation folder
The DLLs are
If you also add all other DLLs your code depends on, you can even compile your code for verification. If you don't copy your .cs file but use the same that is referenced by the unity project, then each time you save the file in Visual Express, Unity will notice the change and reload and compile it using Mono.