I went back to Old Navy yesterday on the way home from school to see if the clearance section here is as good as the one in PA. I was pleasantly surprised. I got two more skirts that I can wear to work for $4 each as well as a new shirt for $4. However, if you're looking for kid's clothes, I didn't see much at the one I went to. The one in PA had a ton (at least until this one couple bought TWO overflowing carts of it!).
They have TONS of stuff on clearance, and not all of it's summer stuff. The only caution, though, is that the prices aren't marked very well. I paid $4 for my shirt, but I saw the same shirt marked $6 or not marked as clearance at all. But, if you have patience, you can find quite a few good deals!