What is the most effective way to file a comsumer complaint against a
company on internet? What I am looking for is someone can help me to
park my complaint letter on the server and consumers can see my
complaint whenever their search results show's the company's name.
This way comsumers will aware this problem.

These sites are popular:

http://www.complaints.com/

http://www.my3cents.com/

A similar question answered:

http://answers.google.com/answers/threadview?id=469080

If you don't mind paying a little money, use <a target="_blank"
href="http://adwords.google.com">Google Adwords</a>. That way your
complaint will turn up when people search the company's name on
Google, not just when they go to a web site like complaints.com.

What you do is set up a blog on <a
href="http://www.livejournal.com/">LiveJournal</a> or something like
that. You only need one entry, telling the details of your complaint.
Then you set up your Google Adwords campaign, pointing to the URL of
your LiveJournal entry, with the text of the ad something like "Learn
how Acme Corp. screwed me over". The keyword of course is just Acme.

The most succesful and popular one is www.planetfeedback.com