Visas are required only by citizens of Colombia, Dominican Republic and Panama. Citizens of other countries can stay three months without a visa. (http://www.haiti.org/)
By plane
International travelers will arrive in Haiti at Port-au-Prince PAP at the Aéroport Toussaint L'Ouverture Airport or Aéroport International Cap-Haïtien in the North. The plane tickets can be purchased via many online ticketing sites and agencies. There are intra-Haiti flights available as well. Prices on these flights can fluctuate from time to time due to inflation but, depending on the airline, are usually between $125-$132 return from and to Port-au-Prince, cheaper between Port-au-Prince and Jacmel. A really cheap, dependable and popular airline is Sunrise AirwaysIn addition to avoiding rather dangerous and inadequate public transportation system by bus and tap-taps, flights offer a safe passage into and out of Port-au-Prince from other parts in Haiti.
Airlines such as American Airlines, Delta and Spirit serve Port-au-Prince from the US. Air Canada, Air France and Caribair, among others, also offer international flights to and from Port-au-Prince.
Lynx Air flies from Fort Lauderdale and Miami to Cap-Haïtien. MFI Missionary Flights International fly to Cap also from Florida, but only registered non-Catholic Christian missionaries are welcome aboard. Other international airlines serving Cap-Haïtien include Sky King, Turks and Caicos Air and Pine-apple Air.
By road
From Santo Domingo, Caribe Tours runs a once-daily bus to Petionville in the hills above Port-au-Prince that leaves at 11:00 am. A ticket costs $40 one-way, $26 USD tax and and 100 DR. Unfortunately, this bus drops you off in Petionville after dark so make prior arrangements with a trustworthy person to meet you and transport you to your lodging.
There is also a crowded border crossing between Dominican Republic and Haiti in Dajabón/Ouanaminthe. The border is open only during the day. From here you can catch local transport to Cap-Haïtien.
Another, less expensive, option from Santo Domingo to Port-au-Prince, is to take a gua-gua Dominican minibus from Santo Domingo departing a few blocks north of Parque Enriquillo for 380 DR pesos about $10, 5 h and arrive in the border town of Jimani. From there, it is a 4 km walk or a 50 DR pesos ride by motoconcho to the border post.
The border is apparently open 09:00-18:00 but don't rely those times. It is very easy to cross the border without submitting to any immigration procedures on either side, and although it would probably be illegal, it saves a few dozen dollars on bribes and is much faster too. Apart from entering the DR when a soldier takes a look at the passport, nobody does any inspection: immigration or customs. Entering Haiti legally is quick: fill out the green form and pay whatever amount the official asks around 100 DR. There are no ATMs at the border.
Moneychangers give gourdes for DR pesos and US dollars. Rates are fair. There is plenty of local transportation from the border to Port-au-Prince. Crowded tap-taps and buses can take you to Croix-des-Bouquets for 50 gourdes 1.5-2 h, from where it is another hour to Port-au-Prince proper bus, 5 gourdes. The road has varible conditions and and is prone to flooding. Peruvian UN soldiers at the border have confirmed that the road to Port-au-Prince is safe to travel with no incidents of robbery or kidnappings, but definitely try to arrive in Port-au-Prince before dark.