Pomodoro is great! Also, have you considered the fundamental of diet? Most ADDers are of the Protein Metabolic type -- which means we are extra sensitive to sugar/carbs (i.e., our brain turns to mush). If you're not getting a protein-based bkfst and lunch, you'll always be frustrated with your mind's behavior whilst sitting at your desk.

If you're already pumping the protein, I've got some "Zen brain hacks" that will help. Let me know if interested...