I recently started using Geektool on my Mac for my background. I can't say enough about it. It really makes my desktop look nice. Apple should really look at incorporating this into the operating system if they haven't already.
One thing I have done that I haven't seen on many other examples is using the Todotxt todo list application for displaying my Todo list right on my desktop. I have it set to update every 30 seconds so it keeps things up to date and lets me know what to do next.
Just create a shell tool and have it run todo.sh. It is very simple and easy with no custom scripts or tools. Using custom shell scripts you could create many lists that display different projects, locations and priorities.
Here are a couple examples.
Tasks to do around the house:
todo ls @home
Stuff to do at work:
todo ls -@home
Buddhist task list:
todo ls @monastery + renunciation +harmlessness +goodwill