OmniOutliner is one of my favorite applications. I use it every day as a planner/outliner. OmniFocus grew out of OmniOutliner, and I used to be an OmniFocus user. But since I started using OmniOutliner I've completed the circle and use it for just about everything, including todolists.

Only big limitation is that it's Mac and iOS only. No web or Windows version (also, the Pro version is a bit expensive)