Can someone suggest me some good and reputable companies or persons who are in business of buying great domain names?

So, I mean that they can be contacted if you want to sell domains. I'm not interested in sites where you can only list your domains for sale so that other can see it. I know for companies like Afternic and SEDO but this time I would like to find companies with whom I could negotiate directly.

It truly depends on the name. Some of the big names frequent the boards and will readily purchase a very nice name if you PM them. Just remember that what you may consider Gold others may consider junk. My feelings (yes I have them) were hurt once when my "prize" domain wouldn't even sell for dirt cheap on the forums. I had spent $$$ catching at Pool and then couldn't even give it away.

I think there is a guy domainguru who might be a good option although never used him

Related Offers and Requests or Domain Name Offers and Requests seems like an appropriate place to start.

Maybe we should recommend the NetProphet

Joking... :D

use big brokers like sedo.com greatdomains.com afternic.com they have representatives which they can talk to you directly.

or use the domain related forums to find those brokers like domainnametalk.com dnforum.com domainstate.com namepros.com domaingator.com domain-chat.com domainnameforum.com etc..