kermatdi.com is the best I've found with my limited research on it. They can get you over 30hp with a tune. Doesn't sound like alot to us but that's a 30% increase on a 100hp car, equivalent to adding 100hp to a DMax.
My fiance is so glad I talked her into her '05 Jetta TDI when she moved to NC. She bought it with 92,000 miles in December and already has 115,000 on it. So far I've changed the oil and one glow plug. For their size they are really comfortable cars for bigger guys to drive - at 5' 11" I can move the seat back far enough to not be able to comfortably reach the pedals, the steering wheel is telescoping, you can "pump" the whole seats up and down. Her's gets right at 50mpg on the highway and over 40 in town. It has enough pep for her but I wouldn't mine giving it another 30+ hp.