Participating Target retail stores offer 10 4x6" digital photo prints for $1. (Click "10 for $1" to see this offer.) Better yet, purchase 50 prints for $5. This $5 printable coupon makes them free. (It's the third coupon over.) That's the best deal we've seen for photo prints from Target. You must order these prints via an in-store photo kiosk; you can't use the online service for in-store pickup.
Update: Target also offers a 8x10" Traditional Portrait for free via this printable coupon.