The ice maker just stopped making ice today. It's made ice great for the past 3 years. Everything else works.

If the water pressure for water through the door is low I would check your saddle valve that taps into the line. I would next check your icemaker fill tube to make sure it is not frozen. If it is then you will need to replace the saddle valve because it is due to low water pressure.
You can try to manually harvest the icemaker by turning the power switch off-on-off-on and then pushing the lever in three times in a row. This will harvest the icemaker. If the icemaker harvests and the rake moves then its most likely still good. (if theres a batch of cubes frozen in the ice maker then its def bad.) If you get it to harvest and no water comes in then you will know its a water supply issue.
Replacing the inlet valve and saddle valve will most likely correct the issue. You may only need a new saddle valve and they only cost about 10 bucks.
Let me know if this helps _MJ_