I remember some stuff about the Rankine cycle. Mother Earth News was holding it up in the late 70s or early 80s as the holy grail of future energy generation. If I recall correctly the OTEC plant, which pulled super-cold water up from ocean depths, used a low differential Rankine cycle.
Yup. Here's more about that:
Ocean thermal energy conversion - Wikipedia, the free encyclopedia
SAAB-Scania did work with turbocompounding for their big trucks and I think they're even available currently, I guess this Rankine system would be a natural next step. I think though that due to space constrictions it would be hard to have one of these systems on anything much smaller than a medium-duty truck; Peterbilt and some others already offer hybrid models and this would free up the engine from having to twist a genny to charge the traction battery. You can see though how it would nicely coincide with the radiator, so it'd be great to put some of that energy back to use instead of just throwing it over the side.