The NYSE trading floor is closed each year for several major holidays. If New Year's Day falls on the weekend the market is not closed for New Years. The 2009 New York Stock Exchange Holiday calendar shows the market closed for:
New Year's Day
Martin Luther King, Jr. Day
President's Day
Good Friday
Memorial Day
Independence Day (July 3rd)
Labor Day
Thanksgiving Day
Christmas
For 2010, the NYSE will be closed for the same holidays. Independence Day will be observed on July 5th because the 4th of July falls on a Sunday in 2010.