The official tourism website of the USA is www.discoveramerica.com. It has links to every US state tourism office and website, plus loads of ideas for itinerary planning.
Most cities and towns have some sort of tourist center that provides local information, typically operated by the convention and visitor bureau (CVB) or chamber of commerce. These entities tend to list only the businesses that are bureau/chamber members, so not all of the town’s hotels and restaurants receive coverage – keep in mind that good, independent options may be missing.
A few websites to get you started:
New York State Tourism (www.iloveny.com)
Visit Florida (www.visitflorida.com)
Visit Louisiana (www.louisianatravel.com)
Visit Maine (www.visitmaine.com)
Washington DC (www.washington.org)