we currently have a lot of exchange where steem can be traded and picking a fix number wont be possible, but what I can do is drop a link that will direct you to a page, showing list of exchanges where steem can be traded
Although the list might not be complete, but it covers a lot
Also, saw tweet today from OnepageX showing that they support steem as well
You can access it here https://onepagex.com/
copy both links to your url page and the information's you need will be provided to you.
Do have a nice day.
There are tons of exchanges where you can trade steem: Here are a few
According to coinmarketcap you can trade steem on the following exchanges: