As a practicing christian I always offer to present an assembly when I visit schools. Not every school takes me up on this but those who do, enjoy it enormously.
Lasting for about 20 minutes I include a song I wrote and performed on a BBC1 multi-cultural Sunday morning programme many years ago. The song is based on the parable of "The Sower" I also use a pre-recorded backing track for a very popular song from Junior Praise. The song is "I may Never March in the Infantry" and involves lots of actions and movements.
This is a very fast paced and uplifting assembly and always has the day off to a wonderful start.