I'm a pretty casual dresser so I spend a lot of time wearing sneakers. Thus, athletic socks are a necessity for me. I look for something comfortable, fairly long lasting and not too expensive. Old Navy socks fit all of these requirements.
I found Old Navy socks years ago in the men's section. The version I like best is the low top cut. The elastic at the top of these socks is not too tight, but not too stretchy either. I've found it maintains the elasticity very well through many washings. The bottoms of the socks are cushioned, meaning that the terry cloth finish on the inside is a bit thicker than the tops of the socks. I think this gives them a more comfortable feel and prolongs the wear of the sock somewhat.
Even though most men's athletic socks tend to come in one size (9-11), those come in a smaller size as well (6-9). Almost perfect for me as I wear a women's size 6 shoe. They are still a little bit big but at least I don't have the dreaded ankle heel that I usually end up with.
Another plus for me is that they are made in the USA! Many of Old Navy's clothes are not made in the USA (I've seen a lot of Pakistan and Indonesia labels). I love supporting a US business even indirectly through Old Navy. They come in a pack of three and are made of a cotton/lycra spandex blend.
I wear these socks almost everyday and I do have to replace them fairly often, but I think they do last longer than other socks I've had.