A handful of races remain to be projected. CBS News estimates that Democrats will win 252 races across the country, and Republicans will win 173 of a total 435 seats.
"It's the night we have been waiting for," said House Speaker Nancy Pelosi, D-Calif., who handily beat back a challenge to her own seat by anti-war activist Cindy Sheehan, running as an Independent.
However, several races across the country remain too close to call.
Democrats are breathing a big sign of relief in Pennsylvania. The self-sabotaging Rep. John Murtha, who was up against former military officer William Russell, retained his seat, CBS News estimates. That's despite some self-sabotaging gaffes, including calling some of his constituents "racist." As a last-ditch effort to keep his post, Murtha called in Democratic "Big Dog" Bill Clinton to campaign for him Monday.
The Republicans' last man standing in New England, Rep. Chris Shays, has been toppled. Polls had shown Shays in an extremely close Connecticut race with his opponent, Democrat Jim Hines of Greenwich. But after Himes rode on Barack Obama's coat tails in this liberal district into the lead, Shays conceded the seat after 22 years in Congress.
"The defeat of Congressman Chris Shays demonstrates more than any other race that larger forces were at work," said CBS News consultant Dan Bartlett, a former counselor to President George W. Bush. "Even good public servants lost tonight."
Democrats unseated six Republican incumbents and captured eight open GOP seats, capitalizing on the large number of Republican departures. Republicans knocked off three Democratic incumbents.
After picking up 30 seats in 2006, a big gain is unusual.
"This is the first time since the Great Depression that the Democrats have had back-to-back pickups in the House, so it's significant," said CBS News consultant Mark Mellman, a Democratic strategist.
One upset that's not part of the rising Democratic tide: Republican attorney Tom Rooney grabbed hold of the Florida seat of first-term Democrat Tim Mahoney. In 2006, Mahoney (a former registered Republican) had barely won the red district after GOP Rep. Mark Foley resigned, having been involved in a scandal over his contact with teenage congressional pages. During this past campaign cycle, Mahoney confessed to a scandal of his own - having at least two affairs, one with a former staffer whom he paid to keep quiet. Now, it appears he will face a similar fate to Foley, and the district returns to Republican representation.
Also good news for Republicans was the bruising defeat Republican Bill Cassidy dealt to Democratic Rep. Don Cazayoux of Louisiana, who had been elected in a special election six months ago.
In New York, a victory in an open seat on Staten Island gave Democrats control of all of New York City's delegation in Washington - for the first time in 35 years. City councilman Mike McMahon won the race to succeed Rep. Vito Fossella, who was forced to resign amid drunk driving charges and revelations that he fathered a child from an extramarital affair. Also, former congressional staffer Dan Maffei won election to succeed retiring GOP Rep. Jim Walsh, becoming the first Democrat in nearly 30 years to represent the district around Syracuse, N.Y.
In another key race, Virginia's heavily contested 11h District, Democrat Gerry Connolly, a local politician, defeated Republican Keith Fimian, a nearly unknown businessman with a steady cash flow. Another party upset in Florida's 8th District: Rep. Ric Keller, a Republican was unseated by Democrat Alan Grayson, a businessman and highly-educated lawyer.
Republican Michelle Bachmann,R-Minn., also narrowly won reelection against Democratic challenger Elwyn Tinklenberg. Bachmann recently made news by suggesting an investigation of House members to determine which held "anti-American" views.
Democrats said they count on capturing more than 20 former GOP seats, and told CBS News that if they pick up 19 or fewer seats, that's just an "OK" night. But Republicans said that if they lose only 16 to 19 seats - given the economy and how it has affected Republicans in the polls, and the huge number of GOP House member retiring this year - they'll be "dancing on the table," CBS News correspondent Sharyl Attkisson reports.
It could be the first time in more than 75 years that Democrats would ride large waves of victory to bigger congressional margins in back-to-back elections. In 2006, they won 30 seats to gain control of Congress in a surge powered by voter anger over the Iraq war.
This year it's the sour economy and public antipathy for President Bush that posed the biggest challenges for Republican candidates. A wave of GOP retirements and huge financial and organizational disadvantages compared with Democrats made a grim fight even tougher.
National Republican Congressional Committee Chairman Tom Cole responded to his party's losses by saying: "This isn't the first time or the worst time for me to be in this situation or for my party to be in this situation."
He said Obama's massive registration effort and organization of volunteers within states helped Democrats pick up seats lower on the ballot.
"The presidential campaign makes a difference and the ability of Obama ... to put a lot of people on the ground hurt us," he said. "I give the Obama camp a lot of credit."
It all adds up to a good night for Democrats. But many of the Democrats favored to win in conservative districts are moderate or conservative-leaning Democrats - known as Blue Dog Democrats. So while increasing the Democratic majority in the House, they may not always vote along party lines.
But CBS News consultant Dee Dee Myers, a former press secretary to President Clinton, said a strong Democratic majority in Congress begs plenty of questions.
"Voters in tonight's presidential election signaled loud and clear that they wanted the new president - and by extension, the Congress - to focus on the economy, the economy, the economy," she said. "But with resources scarce and getting scarcer, what will they choose to do first? And second? And will it help?"
Democrats currently control the House by a 235-199 margin, with one vacancy. Two hundred and eighteen seats are needed for a majority, which Democrats have squared away.
Both parties took in huge amounts of campaign cash in House races, although Democrats had a clear edge. Democratic candidates raised $436 million, compared with Republicans' $328 million, according to federal data compiled by the nonpartisan Center for Responsive Politics.
The parties' campaign committees also bankrolled the most competitive races, with the Democratic Congressional Campaign Committee pouring in $76 million and the National Republican Congressional Committee spending $24 million.