  In my ongoing (and likely neverending) attempts to finally get myself organized, I have just found and installed urlLink Alex King's "Tasks" software.
So far, it's quite nice - it's a web-based app that you could run on your website if you so desired... or, even nicer given Mac OS X's built-in Apache webserver (and if you add PHP and MySQL to that... a relatively simple thing) it'll run locally. It's tree-based so you can add top level items (ie. for various projects) and then add various sub-tasks (and sub-sub tasks) as necessary. Everything that you'd look for in a task manager is included, along with some nice extras such as iCal integration - it will publish any tasks with due dates to an iCal compatible format that you can subscribe to in iCal.
Set it as your startup page in the browser of your choice (excepting of course IE, which I wish people would just stop using already) and voila! Instant organization... or at least the semblance of it accompanied by a minor sense of accomplishment at having installed your first PHP app locally... 
