Here is an hour-by-hour guide (all times Eastern) to the races that will serve as leading indicators for where the election is headed.
7 p.m.: Indiana/Kentucky
There are three House races in the Hoosier State that will tell us what kind of night it will be for Democrats. The 8th District open seat is a certain pickup for Republicans while the 9th District fight between Rep. Baron Hill, D, and lawyer Todd Young, R, is a jump ball. Rep. Joe Donnelly, D, is favored in the South Bend-based 2nd District. If Democrats lose just one of those three, they can hold the House. Lose two and their majority likely is gone. Lose all three, and Republicans will gain upward of 60 seats.
In Kentucky, Republicans are spending money on semilong-shot challenger Andy Barr in the 6th District race against Rep. Ben Chandler, D. If Chandler loses, Republicans could well make a historic number of pickups. Meanwhile, in the Senate race, if state Attorney General Jack Conway, D, can defeat ophthalmologist Rand Paul, R, it would be a major upset for Democrats.
7:30 p.m.: Ohio/West Virginia
Ohio Gov. Ted Strickland, D, is in deep political peril in his race against former Rep. John Kasich, R. The White House would love to see Strickland win because controlling the governor's mansion in a state likely to be very competitive in 2012 could give President Barack Obama a leg up. In West Virginia, popular Gov. Joe Manchin, D, appears to have stabilized his bid for the state's open Senate seat. But, Obama and the national Democratic Party are very unpopular in the Mountain State and that could drag wealthy businessman John Raese, R, across the finish line.
8 p.m.: Florida
The marquee governor's race of the night is between state Chief Financial Officer Alex Sink, D, and former health care executive Rick Scott, R. Both parties have dumped scads of money into the state, and Democrats see this outcome as crucial to their entire night. Also keep an eye on the South Florida 25th District open seat race, a rare opportunity for a Democratic pickup.
8:30 p.m.: Arkansas
Three-term Sen. Blanche Lincoln could be the first Senate Democratic incumbent to fall, when polls close here.
9 p.m.: Colorado/S. Dakota
No race has seen more spending by outside groups — $25 million and counting — than the matchup between appointed Sen. Michael Bennet, D, and Weld County prosecutor Ken Buck, R. Buck has tried to make the contest a referendum on the president, but he has made enough verbal gaffes to give Bennet a path to victory in what could be the closest Senate race in the country.
South Dakota has only one congressional district, and it has produced a close race between Rep. Stephanie Herseth Sandlin, D, and state Rep. Kristi Noem, R. Herseth Sandlin has run a solid campaign to distance herself from Obama in this Republican-leaning state, and the race will serve as a test case for whether moderate Democrats can escape the drag of the national party.
10 p.m.: Nevada
The Senate race between Harry Reid, the most powerful senator in Washington, and former state Assemblywoman Sharron Angle, R, is on course to top $50 million in spending — a remarkable sum given how few voters are genuinely undecided in the contest. Both sides see symbolic importance in this race: A Democratic win would salvage what could be a very tough night while a Republican victory would mark the second time in four cycles the party had beaten the Democratic Senate leader.
11 p.m.: Washington state/Oregon
The race between incumbent Sen. Patty Murray, D, and former state Sen. Dino Rossi, R, in Washington has been tightening recently, but Murray remains very well-liked among the electorate. Rossi is trying to paint Murray as an insider, a potentially potent message in an anti-incumbent year.
In Oregon, former NBA player Chris Dudley, R, has run a strong gubernatorial campaign and is in a nip-and-tuck race with former Gov. John Kitzhaber, D. A Dudley win would give Republicans a much-needed foothold in the Pacific Northwest.
1 a.m.: Alaska
Polls don't close until 1 a.m. in Alaska, where it could take days or weeks to determine the winner of a three-way race for Republican Sen. Lisa Murkowski's seat.
Information from the Washington Post and Associated Press was used in this report.