They Need To Be Fed 2, sequel to the original - critically acclaimed - running, jumping 360 degree gravity platformer, is free - but just for today!
Normally priced at £1.28, the game is available free courtesy of AppTurbo's AppOfTheDay, a great little app which offers a new free title every day. To be fair, quite often the free apps are pretty uninspiring (and i'm not sure they're always actually a deal), but the occasional gem like this one make it well worth an install.
I was a big fan of TNTBF1, so i've downloaded this already and it's excellent! :)
One thing to note is that after the deal has passed, you're not able to reinstall the app... so make sure you get a backup with your utility of choice (e.g. Titanium Backup) just to be safe! :)