I love Old Navy for the basics that you would probably pay twice as much for elsewhere...and also for cute little fun tops or accessories that you don't feel too guilty buying, because they are all reasonably priced.
This year, my must-have was the v-neck "perfect fit" t-shirts in every color. I believe they were about 2 for $15, so at the price, I bought one in every color, and wore them constantly. Also a favorite were the ribbed tank tops. These are the things you wear over and over again, so it makes sense to buy several in different colors.
The only thing I don't like about Old Navy is that their pants don't fit quite right. I usually don't have a problem finding pants that fit....and the ones at Old Navy all fit different. Usually I can find a pair that fits if I try on a ton in the same size, but sometimes I just don't bother.