I am compiling a list of websites used to look up information on businesses. Generally this is the Secretary of State's website. Most of the states have databases that are free to search, but some states still charge for this service.

California
Colorado
Delaware
Florida
Georgia
Illinois
Indiana (basic info is free, extra details require payment)
Kentucky
Louisiana
Mississippi
New Jersey
New York
North Carolina
Ohio
Oregon
Pennsylvania
South Carolina
Tennessee
Texas ($1 per search)
Wisconsin