Inspired by the Olly Hit Snake plugin I wrote something similar for Olly 2. I am calling it DiffSnake.
Basically you use the Hit Trace feature in Olly. Run the hit trace up to some point. Then take a snapshot. Continue running the hit trace up to some other point, then call the diff. You will see a window with all the code addresses called since. The color of the hit trace 'dots' for the new code will be changed to black (from the original red).