Highest city I had in the beta was just under 30k population. Didn't get a screencap of that one but here's a circle city I just made. I didn't get to quite finish it within the hour and for some reason throughout my whole playthrough my Coal Plant was stuck permanently selected.
edit- took a few of the pics out of the thread. Check out my
imgur album instead. Has some pics of a rural town too.
Gas! 