Lots of great choices, but probably not enough for all.
The following are along the route (no detours required).
Colle Val D’Elsa
Monteriggioni
Passignano sul Trasimeno
The following require a slight detour:
Lucignano
Cortona
Castiglion Del Lago
I listed them in order of appearance as you travel west to east. I have bolded the most visited, however all of them are pretty popular destinations.
If you start in the morning you can easily visit two (half day each). Monteriggioni is ultra small and you can see it in a very short time. Although there is a winery with wine tasting inside the walled village, so you might be tempted to stay longer.