Sign up as new member on Educents and get a free $10 credit to use towards your first order. Credit cannot be applied to shipping but if you find a digital item for $10 or less, it'll be totally free because it's a download [and no shipping is needed].
Sign up as a new member on thredUP and you'll get $10 off your first order of practically new women's or children's clothes. You should be able to snag some really cute name-brand clothing for cheap! Shipping starts at $2.99.
If you're a RueLaLa[.com] member, go over and log in. They are dropping FREE $10 credits in existing members' account. If you're not a member yet, you can sign up for free and get in on future free credit promos.