I suggest for the simplest system:

Getting Things Done, by David Allen.

Googling around for the title alone will get you tons of info on it, in fact, he spoke for the company Google and his presentation is on youtube as well.

The book is an easy read and it basically uses lists of next action steps for each project.

I have a blackberry and use it for email etc, but nothing beats a thin memo pad, without dated pages etc, where you just use lists of next action steps for each project.