Paul Del Vecchio has shared a number of aspect mask mattes for use in editing and post production. Aspect ratios available include 4×3/1.85:1, 4×3/2.35:1, 16×9/1.85:1, 16×9/2.21:1, and 16×9/2.35:1. They are free to download and use, so check ‘em out.