How do you choose a good domain name

[goodone]

How does one come up with a good domain name? You know these big companies like yahoo, google, myspace, ebay and so much more!! How did these people come up with such a good idea for a domain name, I personally don't know how they did it but whenever it's time for me to register a domain name, I just go clueless.

I would really like to own a very huge all round company some day but I just don't know what to call it,or rather which domain name to register for it. It is one of my very big dreams to own a very large all round company and although I can't really see my way right now I would like to start by getting a very good domain name, but as I said before I'm kinda clueless. This company would be all in one maybe some thing like yahoo, with free email service, hosting, search engine, news entertainment and much more, through just one domain name.

I would be truly greatful if you guys would help me out here and give me some very good idea for a domain name. And remember guys it should not be too long, it should be catchy and it should be very unique.

Please help me everyone, thanks in advance.