Try the SEC website for publicly listed companies.

I don’t think there’s a national database in the US available online for all corporations. As @bob_ says, you could use the SEC for publicly traded companies.

Usually you’ll be able to find a database for a particular state, such as in this case, California: http://kepler.ss.ca.gov/

Here’s the record for Fluther, for example.

Maybe someone else knows of a national database, but I couldn’t find one and haven’t heard of one. Hope this helps, though.

Actually strangely, that California business search site I linked to is also showing companies in other jurisdictions. I don’t know if they’re covering everything, but I’ve seen corporations registered in a heap of places. Try it.

if you know the state, just go to that state’s secretary of state website. Business entity search is usually a rather prominent link…