Convert from a specifc range to another one
You could use a dual RRO op-amp (eg. AD8676) and ICL7660 as follows (single 5V supply)







simulate this circuit &ndash; Schematic created using CircuitLab

This has 0~5V output for -10~10V in. If you have to handle the -10V and +10V cases with an ADC that has a nominal 5V reference, then you may wish to increase R1 slightly to cover saturation voltage of the op-amps, resistor tolerances and so on, perhaps 5-10%. Then just scale the number from the ADC digitally. 

You can bypass R6 and R7 with 0.1uF if you're worried about noise. 

One advantage of this circuit is that the gain is set by two resistors (input and output gain) so you can change the input range or output range independently. For example, to change to +/-5V input, change R1 to 100K. To change the output to 0~2.5V (say you got a better reference for your ADC but it's 2.50V), change R4 to 49.9K.