A reader has brought to my attention the following remarkable paper:

A. Bentien, S. Johnsen, G. K. H. Madsen, B. B. Iversen, and F. Steglich, "Colossal Seebeck coefficient in strongly correlated semiconductor FeSb₂," Europhysics Letters (EPL), pp. 17008, 2007.

Aparently due to strong corellation and d- character of the bands, FeSb₂ exhibits at 12 K perhaps the largest electrical power factor ever reported:

"S²/rho = 2300 µW/K-cm² at 12 K and is 65 times larger than the value for state-of-the-art Bi2Te3-type thermoelectric materials."

The lattice thermal conductivity is still quite large so ZT ~ 0.005 at 12 K, but with a Seebeck of -45,000 µV/K  the material is bound to be of interest.

Off hand I'm not aware of any other example of such large Seebeck values in anything which might be remotely described as a decent electrical conductor.

 The full manuscricpt can be downloaded for free from the journal's website using this link:

http://www.iop.org/EJ/abstract/0295-5075/80/1/17008