For travelling to Armenia, the citizens of the CIS member-states, the USA, the EU member-states and the Schengen Acquis states do not need Armenian Visa. For the visitors less than 18 years old visa is free of charge. Visa to Armenia is provided by the Representation of the Republic of Armenia, located in the given country (or near it).
The citizens of several countries can get a visa upon arrival in Armenia, at the border checkpoints. In general the procedure lasts 20-25 minutes.
More detailed information regarding visa provision can be found at the web page of RA Ministry of Foreign Affairs.