My favorite Op Amp for those applications is the TLV2470 from Texas Instruments. This is a rail-to-rail unit and almost indestructible. The input impedance is in the Meg Ohm range and the output is a few ohms max. You can drive an ADC directly with it.
You can find a simple gain calculator at this address:
http://www-k.ext.ti.com/srvs/cgi-bin/webcgi.exe?Company={5761bcd8-11f5-4e08-84e0-8167176a4ed9},kb=analog,case=obj(32618),new
A calculator for gain and offset is here:
http://www-k.ext.ti.com/srvs/cgi-bin/webcgi.exe?Company={5761bcd8-11f5-4e08-84e0-8167176a4ed9},kb=analog,case=obj(35457),new

Good luck!