Most visitors from outside Canada and Mexico arrive in the United States by plane. While many medium sized inland cities have an international airport, there are limited flights to most of these and most travelers find themselves entering the U.S. at one of the major entry points along the coasts:
* From the east New York City, Chicago, Philadelphia, Atlanta, Charlotte, Boston, Washington, D.C., and Miami are the primary entry points from Europe and other transatlantic points of departure. All the major east coast airports have service from a few key European cities.
* From the west Los Angeles, San Francisco, Honolulu are the primary points of entry from Asia and other transpacific points of departure. Seattle has some international flights, and Portland (Oregon) has a daily flight to Tokyo. Of course, if you arrive in Honolulu, you must take another flight to get to the mainland. Foreign airlines are not allowed to transport passengers to/from Hawaii or Alaska and the other 48 states (except for refueling and in-transit). If you are flying into the west coast to transit to another destination, San Franscisco airport has a free frequent skytrain linking terminals and short security queues, compared to Los Angeles which will see you exposed to the elements catching a shuttle bus or walking between terminals.
* From the south Miami, Florida is the primary entry point from Latin America, primarily South America. Also, Dallas, Houston, Atlanta, and Charlotte are major international waypoints. From Mexico, most major U.S. airports have non-stop service.
* From the other side of the world New Delhi, India has non-stop service to Chicago, Newark (New Jersey), and New York. Chennai has direct service to New York on Jet Airways. Mumbai has non-stop flights to Newark (New Jersey) and New York. From Pakistan, Saudi Arabia, Uzbekistan and United Arab Emirates you can also fly to New York (JFK). Qatar, and Saudi Arabian fly to Washington, DC, and South African Airways goes to New York (JFK) and Washington, DC (Dulles).
Note that the United States requires entry formalities even for international transit, and the current state of international affairs means that this is not going to change anytime soon. You must have a valid visa to enter the United States if required by your citizenship, even if you are immediately continuing on a flight to a different country. If your citizenship requires a visa to enter the U.S., avoid transiting through the U.S. unless you want to spend time and money to obtain a C-1 transit visa. Further, when booking flights to the U.S. note that you will be required to clear customs and immigration at your first U.S. stop, not at your final destination, even if you have an onward flight. Allow at least 2 hours of stop-over (ideally more than 3) at your first U.S. stop.
By car
As of June 1, 2009, ALL persons wishing to enter the United States by land must possess a valid passport; NEXUS, FAST, or passport card; Laser Visa; or an "enhanced driver's license" (issued by certain US states & Canadian provinces)
Traffic travels on the right hand side (as it does in Canada and Mexico).
If you are entering under the Visa Waiver Program, you will need to pay a US$6 fee, in cash, at the point of entry. No fee is payable if you are simply re-entering and already have the Visa Waiver slip in your passport.
The US-Canada & US-Mexico borders are two of the most frequently crossed borders with millions of crossings daily. Average wait times are 0-30 minutes, but some of the most heavily travelled border crossings may have considerable delays—approaching 1-2 hours at peak times (weekends, holidays). Current wait times (updated hourly) are available on the U.S. customs service website [12]. The US-Mexico border is lucrative for drug trafficking, so vehicles crossing may be x-rayed or searched by drug-sniffing dog. If there is suspicion, your vehicle may be searched. Since this is an all-too-common event, expect little patience from border agents.
By boat
Entering the U.S. by sea, other than on a registered cruise ship, may be difficult. The most common entry points for private boats are Los Angeles and the surrounding area, Florida, and the Eastern coastal states.
Some passenger ferries exist between Canada and the U.S., notably from the Atlantic Provinces to New England, and from Victoria, British Columbia to Seattle.
Cunard offers transatlantic ship travel between the United Kingdom and New York City.
By train
Amtrak offers international service from the Canadian cities of Vancouver, Toronto, and Montreal into the U.S.
By foot
There are many border crossings in urban areas which can be crossed by pedestrians. Crossings such as those in/near Niagara, Detroit, Tijuana, Nogales, & El Paso are popular for persons wishing to spend a day on the other side of the border. In some cases, this may be ideal for day-trippers as crossing by car can be a much longer wait.
http://wikitravel.org/en/United_States_of_America
http://www.joanandersononline.com/blog/