Here's three of my favorites:
Temecula Olive Oil Company . They have a tasting room, but after our big lunch, I opted not to taste some of the interesting olive oils they had for sale. There's a great garden art shop there, too (both just east of Main St.). Then we went on over to the Gallery at the Merc.
The gallery with the exhibit is only open when the theater ticket office is open. Luckily for us that was 2-4 pm. I suggest you call the toll free number to be sure of their hours on the day you want to go. This was an amazing (but small) fiber arts exhibit by regional artists. Well worth the trip.
My SIL and I were home by 3 PM - a nice quilty change of pace. I recommend it.