We've listed a couple of list-making apps in our Life Could be Easier: On the Go series, and I wanted to put in a plug for one we haven't mentioned, but that I have been using a lot lately: Wunderlist. Not only is Wunderlist fun to say, it's also super easy to use and it syncs across all of my devices (android, iPad, desktop, web.) Per Paul Zenke's suggestion, I've been using it to keep my inbox empty (well, close to empty at least) by adding items to my Wunderlist if I need to follow up on them, and archiving them if I don't. I keep a list for each of the collaboratives I'm on and I can view them either by the categories, or by due date. It's really helped me stay on top of things. Wunderlist also has the option to create shared lists which can be useful for collaboration on work projects or for sharing things like grocery lists with your family.
Not least of all, I like Wunderlist because it has a very simple, intuitive, and sleek design. Here's a picture of one of my lists: