The key to my music finding success is: Soundtracks. Not just for musicals, but for any movie that I like that I think might have a good soundtrack. I really liked the soundtracks for "Elizabethtown", "Jerry Maguire", "Marie Antoinette", etc etc.
I also think of bands that I liked growing up, and see if they've release anything since they were really popular back in the day. Chances are, they released something in the last few years that may not have done real well on the charts, but would be perfect for a guard show.
I also take into consideration what type of show my kids feel comfortable doing. Are they able to successfully pull off an upbeat, in-your-face show? Or would they rather do something more dark and impactful? Ask them, chances are, they already have a few ideas for you.