Old Navy has size 0, but in my opinion it runs kind of big. It's more like a 2 than a 0. My favorite is NY & Company. I like that they have different lengths, because I need the petite length. Their pants wash well, too. Ann Taylor Loft has 0, and even 00 which is nice. The funny thing is their 00 Petite/Short says 00PS on the tag. My husband was doing the laundry and asked me, "Why does your size say 'Oops' on the tag?" LOL!
White House Black Market also has 0, but their stuff is almost all dry clean only, which I try to stay away from. Same with Ann Taylor Loft.