homebrew lighttpd plist - works in Mountain Lion - place this in /Library/LaunchDaemons/

homebrew.mxcl.lighttpd.plist

<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE plist PUBLIC "-//Apple//DTD PLIST 1.0//EN" "http://www.apple.com/DTDs/PropertyList-1.0.dtd">
<plist version="1.0">
  <dict>

    <key>Label</key>
    <string>homebrew.mxcl.lighttpd</string>

    <key>ProgramArguments</key>
    <array>
      <string>/usr/local/sbin/lighttpd</string>
      <string>-f</string>
      <string>/usr/local/etc/lighttpd/lighttpd.conf</string>
      <string>-D</string>
    </array>

    <key>Disabled</key>
    <false/>

    <key>KeepAlive</key>
    <true/>

    <key>UserName</key>
    <string>root</string>

    <key>GroupName</key>
    <string>staff</string>

    <key>RunAtLoad</key>
    <true/>

  </dict>
</plist>