Where did the answer "I'm going to Disney World" originate?

During an interview after defeating Muhammad Ali for the heavyweight title, Leon Spix was asked by Howard Coselle, "what are your plans now that you are heavyweight champion?".
Leon's reply was, "I gonna go to Disneyland."

"I'm going to Disneyland" (or maybe Disney World?) was the woman skater who was whacked by Tonya Harding.

http://www.phrases.org.uk/bulletin_board/2/messages/17.html

"I'm Going to Disney World!" and "I'm Going to Disneyland!" are advertising slogans which are the most prominent feature of an advertising campaign famously spoken by players from the winning team immediately after the Super Bowl. They are generally spoken in response to a question from an unseen reporter such as, "You've just won the Super Bowl, what are you going to do now?"

Early years

Disney began the campaign for the Walt Disney World and Disneyland resorts in 1987 for Super Bowl XXI. New York Giants quarterback Phil Simms was the first player to announce he was "going to Disney World" following the Super Bowl. Disney also produces a commercial to be aired during the game with players from both teams and a commercial for the days after the Super Bowl. The ad generally stars the Super Bowl MVP. Disney actually films two ads, featuring the two phrases "I'm Going to Disney World" and "I'm Going to Disneyland" to better fit East and West Coast markets. Super Bowl XXV MVP Ottis Anderson was the first to deviate from the usual script. When asked the question, Anderson replied "I'm dedicating this one to our troops," referring to Operation Desert Storm which had begun a week and a half before the game.

Return of the original phrase

The original phrase returned in 2006 with Super Bowl XL, with an ad showing players from the Pittsburgh Steelers and Seattle Seahawks practicing how they want to deliver the line if they are asked 'the question' by a reporter after the game. Disney also projected the 20-year history of the campaign onto a Detroit skyscraper from February 1-5 leading up to the 2006 game. Super Bowl XL MVP Hines Ward said "I'm going to Disney World and I'm taking The Bus." After the game, Steelers safety Mike Logan riffed on the campaign by referring to a Pittsburgh-area amusement park, saying, "Forget Disney World, I want them to open up Kennywood!"

http://en.wikipedia.org/wiki/I%27m_Going_to_Disney_World%21

We say "Disney Land".

It began (and continues as, except in 2005) a Walt Disney World/Disneyland ad campaign for Super Bowl XXI in 1987. Two versions of the spot were made, to fit the East Coast/West Coast markets.