Was simple in Windows XP but took a little bit of effort for find how to show file extensions in Windows 7. Anyway just in case you need to know, do the following:

  1. Open Windows Explorer, you can do this by opening up any folder.
  2. Click “Organize”, scroll down and click on the “Folder and search options”.
  3. Click the “View” tab.
  4. Scroll down until you see “Hide extensions for known file types”, un-check this.
  5. If you are doing web development you might also want to tick “Don’t show hidden files, folders and drives”.
  6. Click “OK” and now your file extensions will now longer be hidden.