Read LDR with A/D converter with adjustable senstivity
You want high dynamic range... but you don't have enough bits. Here is a hack.

Let's suppose you want to measure your LDR's resistance from 100 ohms to 1 MOhms with decent precision...

Remove the resistors, and replace them with 10nF C0G or film caps. Now...


Set ADC pin to digital output, and output 0V.
Wait 100µs
Set ADC pin to high-Z analog input
Wait for a time delay T
Acquire analog value


Now, depending on time delay T, the capacitor will have more or less time to charge through the LDR. In order to measure a much higher LDR value, simply wait longer for it to charge! This gives you easy range switching without any extra parts or pins.

Other solutions include :


ADCs with more bits
Analog MUX followed by variable gain amplifier
dannyf's proposal above