Best way to iterate folders and subfolders

If you’re using .NET 4, you may wish to use the System.IO.DirectoryInfo.EnumerateDirectories and System.IO.DirectoryInfo.EnumerateFiles methods. If you use the Directory.GetFiles method as other posts have recommended, the method call will not return until it has retrieved ALL the entries. This could take a long time if you are using recursion.

From the documentation:

The EnumerateFilesand GetFiles methods differ as follows:

• When you use EnumerateFiles, you can start enumerating the collection of FileInfo objects before the whole collection is
  returned.
• When you use GetFiles, you must wait for the whole array of FileInfo objects to be returned before you can access the array.

Therefore, when you are working with many files and directories,
EnumerateFiles can be more efficient.