I there, I am trying to determine the heat gain into a stainless steel
wine tank.  Can someone help me determine the R-value or U-factor of
stainless steel?  Is there a table out there listing the R-values of
all types of materials including stainless steel?

I'm guessing you're going to have to provide more info on the tank.

Is it solid stainless, or is there a "cavity", and is that cavity
filled with vacuum, air, some other gas?

You could probably find the thermal conductivity of stainless steel in
a materials handbook.  (say, CRC)  For 316 steel, its around 16 W/m K 
(that's meter, kelvin, not millikelvin).  The thermal resistance in SI
units is then d/k (where d is thickness in meters) or d/16 m^2 K / W
-- in other words a thin walled stainless container basically has no
thermal resistance (R-value is very small).  That's why things like
say a Starbucks stainless steel cofee mug is not solid stainless, but
has an air gap.

Thanks for the help.  The tanks walls are actually solid stainless. 
About 1/4" on the bottom and 1/8" on top.  I think I found the answer
yesterday, which is a U-value of 1.176 BTU/h/ft^2/degree F on a wine
tank.  Thanks again for your help!