I'm not sure if Shapeshift.io would be called an exchange because they just accept crypto-crypto transactions. Purse.io is a service that matches people with bitcoin to those wanting to buy bitcoin. The people buying bitcoin will use their credit to buy items on Amazon, send them to the person with bitcoin, and act as an escrow service to essentially allow people to shop Amazon with bitcoin.
As an added bonus, you get about ~15% discount while using Purse.io.
Here's my referral link. :) https://purse.io/?_r=4QqksC