Most nationalities get 30 days on arrival.
The following nationalities must obtaina visa before arriving
Afghanistan, Albania Algeria, Armenia, Azerbaijian, Bangladesh, Belarus, Belize, Bosnia-Herzegovina, China, Croatia, Cuba, Democratic People’s Republic of Korea, East Timor, Egypt, Georgia, India, Iran, Iraq, Jordan, Kazakhstan, Kiribati, Kyrgystan, Lebanon, Libya, Macedonia, Moldova, Nauru, Nigeria, Palestine, Pakistan, Sierra Leone, Sri Lanka, Sudan, Syria, Taiwan, Tajikistan, Tonga, Turkmenistan, Ukraine, Uzbekistan, Vanuatu, Yemen, Yugoslavia
Nationals from Hong Kong and Macao can enter for 14 days without a visa.
Extending a visa costs around US$25 per month and is done easily.