Carrefour

This is the supermarket I went to when I was in Madrid for more than 2 weeks in February, 2011
«Great» Features
1. Reasonable prices for basic food items — bread, olive oil, milk, juice, yogurt, chips, fruits, cheese. I saved money grocery shopping rather than eating out
2. They have «deal of the day» on some of their items. Almost like Walmart, Ralph’s in the US
3. Organize, clean store
«Not So Great» Features
1. You pay for plastic bags during check out. Bring own reusable grocery bags to save money.
2. Most of the staff do not speak English. You better know the Spanish name of what you are looking for so when you need to ask which aisle to go to you can ask them in Spanish.
3. Grocery items cost more when you compare to the prices of basic foods in US. I had to remind myself I am in Europe. Still cheaper to grocery shop than to eat out every meal.