Google up Azure Dynamics if you want hybrid Diesel medium duty.
One of the stepvan chassis companies is doing hybrid gas, can't remember which one, it may be the same one doing a Diesel hybrid RV chassis (eliminating the genny).
VW keeps toying with a Diesel hybrid Golf 69mpg. Like the above it gets to be cost-prohibitive as a Diesel motor costs more than gas then you add for the hybid system. VW is also releasing (Europe) a Polo (smaller than golf - about the size of 2nd generation Golf) with a Diesel & start/stop system, gets about 70mpg, wish I could get one here.
The recent emissions changes have lowered the mileage on Diesels, glad I have my 97 (reminds me to schedule my 296,000 oil change).