ThredUP - great online consignment store. *edit to add promo code**
I've been really really really happy with ThredUP. I've found a lot of great things for both my boys (pics of my stash below). Customer service is awesome and really helpful. Get free $10 in your account by going through this link:
All my clothes arrived in practically brand-new condition (some were BNWT)...super super happy with them!
SEPT20 is a promo code that's supposed to take 20% off your first purchase - I haven't used it because I'm way over my first purchase, but I've seen it posted a few places. I think it expires tomorrow.