Binance: They have resumed limited user registrations which will be open for a few hours every day and for the limited number of users. Try your luck!
Bitmex: One of the whales of Cryptocurrency exchange. You can do margin trading, if thats your thing.
KuCoin: One of the strongest exchange that also offers mobile app (Android and iOS). They have been constantly updating their mobile app to make it one of the best in the industry.
Huobi: Many new cryptos can be found here. Unique approach and something you should signup for in 2018. Offers Exchange specific coin called HT.
YoBit: Low cap coin heaven