Listpro, Notes, Tasks and WIS bar
I've just begun getting to grips with GTD over the last couple of weeks.
After a bit of playing around, I'm using:
Tasks for next actions
Listpro for projects and checklists (I find it really helpful to have Next Actions and project plans in separate compartments.)
Notes (voice recorder on the ipaq) for capturing ideas when I'm walking the dog, around the house or otherwise away from the keyboard. I find you can take notes one handed even with the slip case on.
WISbar to move effortlessly between Listpro and Tasks.
You need to be careful synchronising listpro: remember that a set of lists is a single file, so it is easy to have changes on both pc and pocketpc at the same time. Then you need to sacrifice one set.
I have a couple of couple of small today addins, tAgenda and Launcher which seem to cover the 80% of Agenda that I'd actually use.