How's this for a good idea for a youth group prayer event: an interactive walk and prayer session through the Lord's Prayer.
My good friend Trey Allen is a youth pastor in Texas. Trey set up seven different rooms at church, each one themed around one line from the Lord's Prayer. The students spent about ten minutes in each room praying and thinking in accordance with the prayer. So, for example, there was a room totally covered in white sheets from floor to ceiling (thus the picture on this post) for the room based on "And Forgive Us Our Sins." That room also had a musical version of Psalm 51 playing (I'm assuming Jon Foreman's excellent song, but the post doesn't say) and verses from Eph. 1 and Ps. 51 scattered in the room. Sounds pretty awesome.
Go read the full explanation here and consider doing something similar with your church.