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
…\Unity\Editor\Data\lib\
The DLLs are
UnityEditor.dll
UnityEngine.dll
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.
Visual Web Developer 2008 Express says that it has "JavaScript IntelliSense" – I haven't tried it but if you prefer JS than you should give it a try!
Today I ran into the site of Lucas Meijer he created a hassle-free way to set up visual studio and unity. Check it out here : http://lucasmeijer.com/posts/one-click-unity-visual-studio-integration/
And a small update here, Lucas has done an updated version of his walkthru for Unity 2.5 and windows http://lucasmeijer.com/posts/visualstudio-integration-for-unity25-itemtemplates/ Cheers, Dave