Joseph, JCS, and Godspell are the three most obvious contenders. Anything beyond that will require some knowledge of your congregation.
To be frank, this is what I hate about threads like this. "Can you recommend a play for one-act competition this year?" Sure, whatcha got to work with? "Oh, you know: high school students." — or — "I need a song for an audition." That's nice; I need a date with Brad Pitt. I mean, without telling us much to work with, anything we suggest is going to be shooting blind.
So let's get to some specifics: who all is in your church that would be performing? Age? Gender? Ethnicity?
http://docandraider.com