Where can you buy contract-free Sprint phones?

hello everyone, as of a few months ago, my phone decided not to work... it was a samsung sph a640
anyway, i wanna buy a new one but my contract ends in october and id rather have a new phone now than wait... so i'm wondering if anyone knows where to buy sprint phones that don't require a contract, so pref. a used one or one that doesnt require a contract... any ideas? id like a nice sleek phone, even better looking than the sph a640 if its not too expensive