[mjevans]

Read the (currently) top post by Ars linking to the Wikipedia page.

There's a table of the currently known public chemistries near the bottom.

There are applications with better power density than Lithium based batteries (at the electrodes), but I don't know about how an overall solution would compare to a gasoline setup.

I think the only fair comparison in such a case would be to have a roughly standard car design and compare complete solutions (currently common petrol / diesel depending on vehicle size, hybrid (electric), full electric (batteries / 'flow batteries' of different types)).