user268: If I am not a miner and would like to put arbitrary data in the block chain, is there currently any method or protocol to get a miner to add it for me?

user5: There is a service named btcmsg which allows you to do this. Here is the announcement in bitcointalk. The website is at btcmsg.staticloud.com.
They use a simple protocol to write and read the messages in the blockchain:

BTCmsg Protocol v1 (2011-09-18)
Each message is represented by multiple payment which is calculated by
  the following algorithm:     

Two first chars for message type ('01' for md5, '02' for ascii).     
Then the message in hex (python binascii.hexlify).    
Split the long string to groups of 4 hex digits.   
Each group of 4 hex (e.g. 2 ascii letters from the message) is     represented by a payment in satoshi (maximum 0xffff=65535).   
The service fee (composed of a fixed part and a variable part times     the amount of small payments required, minus the transaction fee) can be seen within the first transaction.



268: <p>If I am not a miner and would like to put arbitrary data in the block chain, is there currently any method or protocol to get a miner to add it for me?</p>
 5: <p>There is a service named btcmsg which allows you to do this. <a href="https://bitcointalk.org/index.php?topic=47283.0">Here</a> is the announcement in bitcointalk. The website is at <a href="http://btcmsg.staticloud.com">btcmsg.staticloud.com</a>.</p>

<p>They use a simple <a href="http://btcmsg.staticloud.com/btcmsg_protocol_v1.txt">protocol</a> to write and read the messages in the blockchain:</p>

<blockquote>
  <p>BTCmsg Protocol v1 (2011-09-18)</p>
  
  <p>Each message is represented by multiple payment which is calculated by
  the following algorithm:     </p>
  
  <ol>
  <li>Two first chars for message type ('01' for md5, '02' for ascii).     </li>
  <li>Then the message in hex (python binascii.hexlify).    </li>
  <li>Split the long string to groups of 4 hex digits.   </li>
  <li>Each group of 4 hex (e.g. 2 ascii letters from the message) is     represented by a payment in satoshi (maximum 0xffff=65535).   </li>
  <li>The service fee (composed of a fixed part and a variable part times     the amount of small payments required, minus the transaction fee) can be seen within the first transaction.</li>
  </ol>
</blockquote>
