Argh, the way you say "Mom clothing" makes it sound frumpy already. I don't wear Mom clothes, I wear woman's clothes, nothing Momish about them. Wear what looks good for your age and body whether you're a Mom or not.
Anthropologie, Macy's, Lucky Brand, Black/White Market are my main spots. I go to Forever 21, H & M with my daughter and get great layering shirts (tanks, T's, long sleeve) for super cheap. They don't last long but it's great to have brand new tank tops for layering for only a couple dollars, I just buy new after a year or so.
Anthropologie always has a sale room, TONS of cute stuff marked way down. Same for Lucky both online and in stores. If you're on a budget don't discount some of the pricier brands, you'd be surprised how reasonable they are on sale. Marshall's is great for a deal as well.
Have fun, wear what feels good!
PS- I almost forgot... some of my family's favorite items are from thrift stores. You need to spend a little more time but you'll find things you can't find in stores and you can't argue with the price.