wait! I meant lin-log converter

[Eric at Svetlana Electron Devices]

Sorry to butt in....I just had to remark on this:

http://www.burr-brown.com/Products/DataSheets/4127.html

It's a log-antilog amplifier. Supposed to be highly
temperature-stable. Has matched transistors and temperature
compensation built in.
I know, it's an expensive hybrid IC. Perhaps some of the readers
are willing to save themselves lots of trouble and just buy
and uses this instead of finding mateched transistor pairs, 
thermistors, etc.

And if that doesn't do it, there's also:

http://www.burr-brown.com/Products/DataSheets/LOG100.html