I checkout out Aldi once and left without buying a thing. They have brands I've never heard of...I would rather buy Walmart Great Value brand. Plus it's not that close to my house.
I do go to Trader Joe's about once a month to stock up on a few things that they carry that are good and cheap. The rest of the time I get staples (bread, pasta, canned, frozen) at Super Wal-mart and meat/fruits/veggies at Harris Teeter (preferably on sale).
Most of our dinners for 4 are under $10. Sometimes as low as $5 (sometimes we have egg-based dinners). But when you add in oatmeal/milk/cereal for breakfast and peanut butter/lunch meat/bread for lunches, not to mention lunchbox staples like juice boxes, carrots, apples, granola bars, we would be hard-pressed to spend less than $100/week. Our grocery bill for a family of 4 is about $600-650/month, but that includes paper products, dog food, and hygeine items (shampoo, etc.) so I think that's pretty good. We probably spend another $100-125 on dining out, and that's a month where we're being "good".