BlockTrades is a website that offers users to directly purchase STEEM or STEEM DOLLARS (SBD) with Bitcoin or a different altcoin from many supported without the need of registration.
You just need choose the crypto coin you with to use for payment from the following supported ones: Bitshares 2.0, Dogecoin, Dash, Bitcoin, Litecoin, MUSE, Ethereum, NuShares, NuBits or Steem.
Then select the crypto token you want to purchase for example STEEM or STEEM DOLLARS and you will get an estimate value on how much you can get for a given amount of coins
The last thing you need to do is set Your Steem receive address where you need to type your steemit.com username
Click on the blue Get Deposit Address Button
You will recieve an address to send BTC or any other payment currency you have selected from the supported ones, both a text address as well as a 2D barcode that you can scan to get the address.
All you have to do is send a given amount of BTC to the coin you chose and upon confirmation of the transaction (1 confirmation needed for Bitcoin) the amount of BTC you sent will be converted to STEEM or STEEM DOLLARS and transferred to your steemit.com account.
Note: You can apparently reuse the address for sending more coins and getting them transferred to STEEM or Steem Dollars and sent you your steemit account, so you can note down the address for future trades.
BlockTrades has another interesting feature, it allows you to directly purchase STEEM POWER apart from STEEM or STEEM DOLLARS and it really works, tested and confirmed. The price of STEEM and STEEM POWER in the platform is the same, so it just saves you some time as when the transaction is confirmed you actually get the purchased tokens directly credited as STEEM POWER in your wallet.
This useful feature essentially saves you some time as when you purchase STEEM and you want to have it converted to STEEM POWER you will need to go to your account's Wallet and have to use the Power Up feature. So if it is STEEM POWER that you are after the feature that BlockTrades offer can be useful compared to other exchanges such as Bittrex and Poloniex where you can only trade STEEM and STEEM DOLLARS
Other useful Guides for trading STEEM: