In Virginia, Republican Bob McDonnell was projected to win by a wide margin over state senator R. Creigh Deeds, a Democrat. McDonnell will be the state's first Republican governor in eight years.
Democrats were expected to win a closely-watched race for a Congressional seat in New York's 23rd district. Democrat Bill Owens is projected to win a special election for the seat over surprise contender Doug Hoffman, a member of the state Conservative Party, according to the AP and major news networks.
The contest in the heavily- Republican 23rd congressional District in rural northern New York catapulted into national headlines in its final days after Republican candidate Dierdre Scozzafava withdrew from the race and threw her support behind Democratic candidate Owens after accusations that her positions on key issues were too liberal.
The political drama highlighted divisions within the Republican Party as it looks to revive itself after tough 2008 election losses.
With 88 percent of the precincts reporting, Owens had 49 percent of the vote to 46 percent for Hoffman. Scozzafava still picked up about 6 percent of the vote.
The Republican victory in New Jersey deals a particular blow to President Barack Obama, who campaigned heavily for Corzine. Republicans have not won a statewide race in New Jersey since 1997.
Christie earned 49 percent of the vote to Corzine's 45 percent, with 99 percent of precincts reporting.
The Virginia, New Jersey and New York races were among a handful to grab national attention during this off-year election season - and seen by some as an early litmus test of the Obama administration's agenda. Mayoral races and referendum ballots also garnered headlines.
Democrats claimed big political victories in 2006 and 2008, including President Obama's win in the traditionally GOP commonwealth of Virginia.
Polls in Virginia favored McDonnell going into Election Day. He appeared to control some of the top issues for Virginia voters, namely the economy and health care.
NewsHour senior correspondent Judy Woodruff, who moderated a debate between McDonnell and Deeds in February, said the major issues of the campaign revolved around how to improve the economy and bring jobs back to Virginia, solving state budget woes and how to fix the state transportation system.
McDonnell succeeded in part by crafting a "disciplined economic message and a campaign that steered clear of the hot-button social issues that in recent elections had alienated voters in northern Virginia and other urban centers," the Washington Post reported.
According to AP exit polls, more than four in 10 voters in Virginia said their view of President Obama factored into their choice on Tuesday. And after more than a year of recession, the economy trumped all other issues for voters in exit polls.
Among the referendums being closely-watched Tuesday was a Maine ballot known as "Question 1," which asked voters to decide whether to repeal a same-sex marriage law signed into law in May by Democratic Gov. John Baldacci that made such unions legal in the state.
If voters uphold the law, it will be the first time the electorate in any state has endorsed marital rights for same-sex couples.
Early returns indicated a close contest, as many had forecast. With 417 of 608 precincts reporting, 52 percent were opposed to same-sex marriage and 48 percent were in favor, according to an AP report early Wednesday.
At the White House, meanwhile, the president was described as not watching the election returns, and spokesman Robert Gibbs earlier dismissed the impact of the governors' races on Democrats and the 2010 elections, the AP reported.
"I don't believe that local elections in New Jersey and Virginia portend a lot about legislative success or political success in the future," Gibbs said.
In other Virginia races, Republican Lt. Gov. Bill Bolling won re-election over Democrat Jody Wagner, and Kenneth Cuccinelli was elected attorney general over Democrat Steve Shannon, according to AP projections.
Find more coverage of the Virginia race, including links to the state's electoral board, at WAMU and track coverage of the New York and New Jersey races at WNYC.
---- Compiled from wire reports and other media sources