[Grocery stores seem to be fairly regional, so if you are from New England you'll probably get more from this post than others.]
I made an interesting discovery a few months ago. It seems that Wal-Mart has excellent prices on some food staples. It's generic brand of cheese, milk, canned vegetables, and beef jerky just can't be beat. Even if I were to buy them in bulk at a warehouse store, I think Wal-Mart beats them. This is a little surprising to me. I always thought of Wal-Mart as a replacement to Bradlees, Ames, Caldor, and Zayre - 4 businesses that have gone under selling typical household items. So you can see why I wouldn't think of going there for groceries.
Wal-Mart is still relatively new to Boston area - I wonder if people have really figured it out.
Next: When is frugal too frugal?