Canon - 4 in 2 (SATB or 4-part choir). Simple and effective, with bright and cheerful Mozartean eloquence. One of those that sounds much harder than it is and perfect for your "Summer Choir." Text from Psalm 100, "Make a joyful noise to God..."
Make a joyful noise to God, all ye lands. Serve with gladness; Draw near to God with a joyful heart. Come before God's presence with singing; Into His gates with thanksgiving, His courts with praise.