www.steemd.com
It's like the blockchain browser of steem, and you can read all the content in steemit.com, but with a more plain style, it's suitable to use it at office!
www.steemt.chat
You can chat with other steemians in different channels, or promote your posts, very powerful!
www.steemdown.com
You will know which whale is powering down or cashing out here.
www.steemdollar.com
You will find the vote power of any ID.
www.steemstats.com
A lot of statistics about steemit.
www.steemstroy.com
A very interesting website that record all the history of your ID, in the format of a story.