Ian is the Scottish name equivalent to John, meaning "God is gracious." Not really used until the late 19th century, it is pronounced EE-an and has a slew of real life and fictional namesakes such as Ian Somerhalder, Ian Harding and the character Ian O'Shea from the recent movie "The Host." Ian Flemming created James Bond. Iain is the typical Scottish Gaelic spelling, and Eoin is another form of John (although it leads to Owen).
Ian currently ranks at #78 in the U.S. top 1000. It is still very popular in its native country, and easily pronounced world-wide.