Don't write your own project management app unless that's what your idea is. IMO.
I really like OmniFocus but it's pretty expensive, and you have to purchase separate licenses for the iPhone, iPad, and OS X versions.
TaskPaper is popular. I tried it and found it too limiting after getting used to OmniFocus.
I really like OmniFocus actually. That's my recommendation for task management software. It's very fast to CTRL+ALT+Space and enter new tasks(whenever you have an idea come to you, just enter it and it will go in your inbox and you can organize it later) and it's easy to keep everything organized. I put almost everything I do in there -- I even have a weekly recurring project to clean my apartment up.
Now, OmniFocus has a breaking point -- it's really for personal productivity, it's not a bug tracker, and it's not for collaboration. If you start growing your business and have other people working with you, you'll need something else... but for solo projects and keeping your personal life organized I really like OmniFocus.
Edit: oh, yes, for teams http://asana.com/ is good. I tried TaskPaper and keeping the document in a Dropbox share -- didn't work too well. The first time we heard "where the hell did my changes go?!" it was time to drop it.