There is so much valuable information on ultimate fitness now online.
I have discovered lots of new ideas through Skyd.
Tim Morrill and Melissa Witmer make use of videos to explain how to build fitness for ultimate. They are both professional fitness trainers and ultimate players, who have investigated how to improve your conditioning specifically for ultimate. I haven't seen many others who can claim all three of these things, and are sharing their stuff with the world.
Here's a taste.