Visual Studio tooling will create “Models”, “Views” and “Controllers” folders in any new ASP.NET MVC 2 Area.
What else should go into this folder? Would you (for example) place custom ModelBinders in Areas/MyReallyGreatArea/Binders if they are only referenced in MyReallyGreatArea?
What is the best practice?

Yes, when I a custom
ModelBinderinMyReallyGreatAreaonly I put it – as you suggested – into a folder within that area, e.g.Areas/MyReallyGreatArea/Binders. When aModelBinderis later used by a different area I then move it up into a folder namedAreas/Shared/Bindersor similar. That way I keep classes located close to where they are used. Why bother with the customerModelBinderifMyOtherEvenGreaterAreadoesn’t use it?The same applies for everything else. If it is used by
MyReallyGreatAreaonly it will be located in there. If it is shared with a different area I put it intoArea/Shared(and possibly properly named subfolders in there).While this is likely to be only a minor issue if you work alone on this project or when then the project is still small, a well thought-through structures pays off as the project grows or as a larger team works on it. In some cases different areas are even worked on by different teams.