there are a lot of exchanger that offer you that kind of service,
for example Kraken,Bitmex,Poloniex and etc etc.
Kraken is a good exchanger and it's very easy to use,but it has a weakness in their website response.
when the price is jumping in,it's very hard to connect to their website and sometimes you can not access it at all.
but other than that they are very good company/exchanger.
Poloniex is a bad exchanger in my opinion,because a lot of bad thing happen in there such as blocked account,
withdrawal issue and else.but their website is very responsive and you can find a unique feature in there.
Bitmex it is not really well known,but in there you can use up to 100x leverage,and they are only doing 1 withdrawal everyday at the same time.
which is prevent hacker to hack their wallets.
do your own research,and make sure to choose the best and the better one for yourself,
and always read their rule and term before doing any trade
I agree that poloniex is bad. They often block their users' account without obvious reason and it seem that they just want to take the money out of the account (?). You can see so many people complaining in their service discussion thread as well as their media accounts.
I hope they could resolve it ASAP but don't really sure people would put their trust on this exchanger or just go to another one.