While some i Pod copying software won't transfer all of these kinds of files (especially if they're not all on your i Pod, i Phone, or i Pad when you try to copy it), the methods above that include drag-and-drop copying of files from one i Tunes folder to another will move these non-music files, too.
After you've moved the files from your old i Tunes library to the new, merged one, take these two steps to make sure that your new library is optimized and stays that way. Then go to Library - Organize (or Consolidate) Library. Next, ensure that i Tunes is set to always organize/consolidate your new library.
This contains all music, movies, podcasts, and TV shows.
Select the folders that you want to move from the i Tunes Music folder (this is usually the entire folder, unless you want to select only certain artists/albums) and drag them to the "Library" section of i Tunes.
Unlike the external hard drive method above, these programs let you retain star ratings, playcounts, playlists, etc. (If you don't, I'd recommend starting before a hard drive failure makes you sorry you didn't.