Really, the best thing out there is a text editor, like Notepad or Textpad - set it so that each line is on its own line.
If you want to search for specific things, use the search function. I'm hesitant to use any pre-built parser, as I like to see everything.
One useful little tool is grep, which will take a regular expression(pattern) and match it, displaying only the lines that match it.
I knocked up a web based one a few months ago at:
http://xtsl.net/php/grep.php (Its basic and very very simple).
If you want to steal the code to host it elsewhere/improve(an easy task) upon it, its at:
http://xtsl.net/php/grep.phps