Clear is an extremely simple (and extremely awesome) to-do list app. I use it every day, and today, the iOS app is free. (Usually, it's $5.) GO GET IT. Sadly, the desktop version is still $10. But give the iOS app a try.
Seems similar - but not as cool, IMO - to Do It (Tomorrow), which is free, available for iOS and Android, has Google Task syncing (which I think is $5) and has an excellent webapp that it syncs with (free): http://tomorrow.do
(I'm not affiliated in any way, just throwing another option out there)