I am an Orthodox Christian. If you marry outside the Church - either in a civil ceremony or in another Christian body's ceremony - you've excommunicated yourself. Period. The usual remedy to this is to get married in the Church, but some Orthodox make unfortunate choices in spouses and marry someone who doesn't want a thing to do with an Orthodox ceremony.
You also cannot marry someone in the Church who is a non-Christian - you can only marry other Christians baptized in the name of the Trinity. So, someone cannot remain an Orthodox Christian in good standing with the Church and marry a Jew, a Muslim, etc.
If an Orthodox does marry outside the Church and doesn't or is unable for some reason to have their marriage blessed in the Church (such as if they married a non-Christian), sometimes the bishop will allow the person to receive the sacraments again, but it can be YEARS.
In addition, if you're an Orthodox not in good standing, you cannot serve as a godparent, as a sponsor at a wedding, be buried from the Church, etc. This is a very serious matter.
The Roman Catholic Church also requires its members to be married in the Catholic Church to remain in good standing with the RCC. However, there is one exception - with the permission of the local Catholic bishop, a Catholic can marry an Orthodox Christian in an Orthodox ceremony - and the Catholic remains in good standing with the RCC. It has even been suggested by the North American Orthodox-Catholic Dialogue that all Orthodox-Catholic marriages take place in the Orthodox parish since that's the only way the Orthodox half of the couple can remain in good standing in their Church.
From the US Conference of Catholic Bishops website:
http://www.usccbpublishing.org/clien...fs/7-050BI.pdf
Other denominations vary. Others might prefer their members get married in a religious ceremony, but it won't put your standing in the body in jeopardy.