These take pre-created playlists and evenly shuffle them together into a new playlist. You can make a "battle of the bands" playlist, alternating between bands. You can shuffle 5 genres (for example, Jazz-Country-Rock-Folk-Metal) so that every 5th tune is a jazz tune. Perhaps you'd like to alternate between new tunes and old tunes, your wife's favorites and your favorites, etc. These scripts make this easy to do.
(Note: In order to launch this PowerPC-era script on an Intel machine, it must first be opened and then saved using AppleScript Editor, which is located in your /Applications/Utilities/ folder. More information is here.)
Sort purchased tracks into discrete playlists by name or account ID
Copy selected tracks or playlist to a new iPod, iPad, or iPhone playlist
Convert selected tracks and replace them with converted versions
Remove iTunes tracks disassociated from files
Apply selected CD's CD Text to its disc and track tags
Exports and then re-imports selected tracks' artwork