One is called 'Tao of Jeet Kune Do' by Bruce Lee (it is a collection of all his personal notes on JKD with a foreword by Linda Lee). The other is 'Jeet Kune Do' by Tuttle Publishers as part of the series of books produced by John Little on many aspects of Bruce's life.
I think 'Jeet Kune Do' is described to be a continuation of 'Tao of Jeet Kune Do' but they both seem to be derived from Bruce's notes and contain almost exactly the same information. I bought both ... which I now regret. Stick with your tuttle book, it is pretty much 'Tao of Jeet Kune Do'. Stick with one is my advice on this one, whichever...
I guess the differences are different arrangements and that 'Jeet Kune Do' contains a large number of photos of Bruce Lee from films and training to illustrate the techniques described whereas 'Tao of Jeet Kune Do' only contains Lee's own sketches. There are only some of these in 'Jeet Kune Do'. I just also noticed that 'Jeet Kune Do', contains less on other arts and is more geared towards JKD. It contains some good summaries on what Bruce thought of other arts but doesnt contain his studies into them, like the stuff in 'Tao of Jeet Kune Do' on Savate for instance. Also, finally just looking through 'Jeet Kune Do' doesn't contain the short part about limb manipulations and grappling. But other than that...

I think one of these two books is enough. I also highly recommend 'The Art of Expressing the Human Body' in the series which tells of Bruce Lee's physical training schemes ... not only outlining his routines but you can see their evolution. Also you can see the exact workout he used to do before filming 'Enter the Dragon'.
