Kevin would like to get organized and wants a good program to be able to make lists and order them in priority. Leo says there are as many options as there are people. On iOS there's Things, which is about $10, and Leo likes it. Things uses the Getting Things Done methodology. Ideally, Kevin will want one that will work across platform.
There's also OmniFocus. What Leo's discovered, though, is that people like to create methodologies to get things done, but not necessarily to get things done. In the end, the simple principal is to get stuff you have to do out of your head and into a custom interface to manage it.
A simple and elegant one is called Clear. It's only $5, but it doesn't have a desktop component, and it should.