One of those is Peterbilt. Peterbilt offers a hybrid system developed by Eaton on some of their class 6, 7, and 8 medium and heavy duty trucks. The class 6 and 7 trucks are are eligible for tax credits of $6,000 and $12,000 respectively. These machines won't fit in most garages but if you have a need for a utility boom truck or you need to deliver furniture, these vehicles should save you some money on fuel costs. You can even get a class 8 tractor trailer with the hybrid system. Interestingly, unlike any of the current crop of automotive hybrids, the Peterbilts actually use lithium ion batteries. No plug-ins though.
[Source: Peterbilt, thanks to Mike for the tip]