When looking at battery tech for (PH)EVs, I came across an interesting experiment converting a school bus into an electric vehicle.The battery used here is a ZEBRA (NiNaCl liquid salt) battery pack. These guys paid $53,500 for their 107 kWh ZEBRA battery (in 2003). In volume production, the manufacturer price sheet goes to about $20,000 for the same battery pack. Lots of benefits here over other battery technologies, most notably its cost, it's robustness, safety and its absense of 'rare' metals. Nickel and table salt (NaCl) are the main ingredients.
Technically, school busses (and city busses and most delivery vans) seem to be a great early adopter to become "electrified", not just because of their frequent stops (regenerative braking advantages), and air pollution (noone likes stinking diesels in urban areas), but also because they run short trips (no more than one day at a time).
ZEBRAs seem to have a very bright future in PHEV tech.