The Pisaq market is close to the Scared Valley and Sacsaywaman. Many tour buses which go to the Sacred Valley may make stops here as well. Remember that the markets are only open Sunday, Tuesday and Thursdays from 9am - 5pm.
The best day to visit is on Sunday. It is on Sundays that the locals set up a mercado de treque (trade market). This market dates back to the ancient Peruvian days where Peruvians in the highlands depended on trade. The natives trade vegetables, herbs and potatoes for other goods like matches, oranges and medicines. Excellent pictures can be taken of people in their native dress and of the colorful fruits, vegetables, dyes and spices.
Also, on Sundays there are masses held at San Pedro Apostol de Pisaq at 6am and 11am. You can see Peruvian people walk out in their Sunday best after mass. When mass is not going on you can check out the church. You can see interesting colonial paintings inside.
On Tuesdays, Thursdays and Sundays, you can go to the Pisac artesian market. Here, you can haggle for goods such as carved gourds, carved chess sets, alpaca goods, weaved blankets and other goods. I have no haggling skills, it seems. For a statue I liked, I thought I got a good price of 60 sols for which 120 sols was being asked. However, other friends in my group were able to get the same statue for 40 sols. It would seem the sellers ask for 75% more for their goods. Another tip is that if you buy different goods at the same stall you can get more of a discount as well. Look for stalls that are not in a central area, the people here will give you more of a discount to buy their goods.