I'm a big fan of taskwarrior, a CLI todo list for linux. I find I use it more than web based ones as I'm always in the console so there's little mental mode switching to use it. Basically not having to go to a browser or touch the mouse makes all the difference.

I'd love it if someone made a todo web app that could sync with taskwarrior. You then get the online slick interface of the web app with the low friction accessibility of the console interface when in the zone at work.