The Arizona Senate race is probably the contest getting the most national attention.
Congressman Jeff Flake, the Republican and former Surgeon General Richard Carmona, the Democrat, are locked in a tight race, vying to fill the post being vacated by retiring GOP Sen. Jon Kyl.
One way to judge the interest and the closeness of a race is to tally the money. Both of these candidates, combined with the Super Pacs, have poured around $20 million into this race.
Jeff Flake voted with his wife at the precinct just down the street from his home. After surviving a contentious primary against businessman Wil Cardon, Flake entered an even more aggressive general election against Carmona.
"We ran a good campaign and I think we have the right message and that is why it is going to be a great day today," said Flake. "I think that we have spread the message and doing it again I wouldn't do it any differently."
Also on Tuesday, a group of children rallied and knocked on doors in support of Flake and Mitt Romney at the corner of Priest and Elliot in Tempe.
Flake has a reason to be a little confident -- almost all the polls in his race have shown him with an average lead of about 5 percent. He's best known for his fierce opposition to "earmarks" -- special requests for federal dollars for local pet projects such as roads and bridges, while Carmona has touted his resume -- a career as a medical doctor, military service in Vietnam and law enforcement experience.
Carmona says, "Today's going real well. I'm just overwhelmed with the passion of the volunteers and the community workers collecting thousands and thousands of ballots, knocking on doors..one group in west Phoenix did 43,000 doors over the weekend. You know, it's just incredible and it inspires me to even work harder."
Democrats recruited Carmona to run for Kyl's seat after it became clear that then-Rep. Gabrielle Giffords wouldn't campaign because of head injuries she suffered during the January 2011 shooting rampage in Tucson.
Carmona switched his party registration from independent to Democrat late last year.
Video: FOX 10's Andrew Hasbun has more on Flake at the Republican Headquarters and Anita Roman covers the Carmona campaign in Tucson.
The Associated Press contributed to this report.