Cover Orange HD (iPad only), by FDG, $1.99 --> FREE!
FDG Entertainment tweeted this morning that "Cover Orange HD is free today and for a limited time only!" If you don't see it free right now, wait a bit as it'll definitely be free later.
Absolutely worth the download for iPad physics puzzler fans! One of my favorite games on any platform, and one I've owned since it first came out and still play regularly.