wpdo

This plugin can log the breakpoints into the file.
<ul>
<li>To check the log, ssh to server, run <code>tail -f /your_wordpress_path/wp-content/debug.log</code> to watch the output.</li>
</ul>
<h4>API</h4>
<ul>
<li>
To log, use <code>defined( 'debug' ) && debug( 'your content to log' );</code> in your plugin/theme code.
</li>
<li>
To log only in advanced debug level, use <code>defined( 'debug' ) && debug2( 'your content to log' );</code>.
</li>
<li>
To log with backtrace depth = 4, use <code>defined( 'debug' ) && debug( 'your content to log', 4 );</code>.
</li>
<li>
To append one variable (usually an array), use <code>defined( 'debug' ) && debug( 'your content to log', $var_to_check );</code>.
</li>
</ul>

DoDebug

soap_media

DebugWp will place a new toolbar at the bottom of your wordpress site only visible to Administrators that shows information about any particular page you are looking at. 
The WordPress Debug information includes :
<ul>
<li>Total Queries</li>
<li>Execution Time</li>
<li>Object Information</li>
<li>Page Type</li>
<li>Front Page</li>
<li>Post Type</li>
<li>Page Template</li>
<li>Queued Scripts</li>
<li>Done Scripts</li>
<li>Loaded Scripts</li>
<li>Loaded Styles</li>
<li>Site Information</li>
<li>Bot Status</li>
<li>Posts Per Page</li>
<li>Active Theme
 </li>
</ul>
You can read more about <a href="http://www.soapmedia.co.uk/debugwp-wordpress-debugger-for-developers" rel="nofollow ugc">DebugWP on our blog article</a>

debugWP

A Plugin for Wordpress that displays additional information to help the developer.

DoDebug vs debugWP