How to plot the open-loop gain of an inverting amp, difference amp, and low pass filter?
Kevin - the term "frequency response" tells you how the gain and the phase depends on the frequency of the incoming signal. However, now we have to discriminate between two alternatives: "loop gain" (gain properties of the open loop) or "closed-loop gain".
Of, course in both cases the results of all three circuit alternatives (as mentioned by you) will be different because the feedback path is not the same.

In case of an inverter, the feedback path is a simple voltage divider (two resistors) and in case of a lowpass it is a frequency-dependent circuitry (at least one capacitor). 

Remark: It is important to be familiar with the terminology:


open-loop gain: Gain of the active device WITHOUT any feedback;
loop gain: Gain of the whole open loop including active device and feedback circuitry;
closed-loop gan: Gain of the complete circuit with feedback applied.