How should I register my business

My friend and I have been working as independent energy consultants for about a year now and we are planning to incorporate to be able to extend our services. We both got our PhDs last year and we want to eventually make a research facility that can develop and sell new technologies.
My quick question is that in order to register our company what should we do. And what type of company should we register in order to be able to easily expand it.

If you are referring to registering your business in the U.S., your state's Secretary of State is the way to go. (Specifically, check out this link courtesy of Joel. )

There are enough dynamics to merit another post altogether on whether you should list as an LLC, S-Corp, etc; you should spell those out in another question or expand on them here for advice.

What answer you expect biven you dont even consider saying where you live ;)

Ask you chamber of commerce, they will know. Ad hey will even give you some advice. More advice comes from a lawyer.

And it may be you have problems - as you were running an illegal not registered business for a year ;)

Agree with mfg, hard to answer without more information and warrants another question. And here's another pretty good resource to start with for learning about the different entity type choices.