Cheddar is by far the best, simplest and most beautiful tasks app, ever.
I use Cheddar for everything and I highly recommend you at least give it a shot. Cheddar is free although if you want some little extras, it's only $19.99 (per year) to upgrade. You can't argue with that.
As well as a web app, Cheddar is available on iOS and coming soon, a Mac app.