The most mature crypto exchange on the market. The user experience is fantastic. From design to functionality, Cex.io works as good as it looks. Currently, they only support a few currencies but they're actively polling their users to add new trading pairs.
Coinbase is a stable, well-designed platform for buying and selling cryptocurrency. The founders have intentionally chosen stability over feature bloat. Long waiting periods for funding, few supported currencies and premium fees might deter some users but the overall experience is perfect for beginners.