By Congresspedia assistant editor Avelino Maestas [3]

A trio of states will hold nominating contests tomorrow, and some of those primary elections will be more important than others. For instance, two Colorado [4] districts have open seats, and the primary winners will probably carry those districts come November. Meanwhile, in Connecticut [5], two Democrats are vying for the chance to take on Rep. Chris Shays [6], the lone Republican from New England in the U.S. House. Nevadans [7] are also heading to the polls, and a cadre of Ron Paul’s supporters has helped drive support for a challenger to Rep. Dean Heller [8] (R) in the 2nd congressional district.

The battle for Connecticut [5]’s 4th CD may be one of the most closely-watched races in the country come November. Democrats in 2006 were able to flip two House seats in Connecticut, leaving Shays as the only Republican member of the state’s delegation. Shays won a hard-fought election in 2006, and 2008 will be no walk in the park. Democrats endorsed Jim Himes [9] at a convention in May, but Lee Whitnum [10] has forced a primary tomorrow. Himes has a large fundraising advantage over Whitnum and the support of national organizations that have targeted Shays’ seat.

The other candidates for office in Connecticut are all unopposed in their respective primary elections.

For more on Nevada's and Colorado's faces, click through.

The number of congressional Republicans retiring this year is creating some interesting down-ballot races. For example, Colorado [4] Sen. Wayne Allard [11]’s decision to step down prompted Rep. Mark Udall [12] (D) to campaign for Senate.

Udall’s seat in the 2nd CD is therefore open, and a trio of Democrats has stepped forward in the heavily-blue district, breaking records along the way. Boulder entrepreneur Jared Polis [13] spent $5 million of his own cash to compete tomorrow, a record for a House primary. His competitors, environmentalist Will Shafroth [14] and former state Sen. Joan Fitz-Gerald [15], have raised so much money that the race has been the most expensive in U.S. history. The winner is expected to prevail over Republican Scott Starin [16] come November.

Colorado Republicans have their own hotly contested races Tuesday. In the 5th district, Jeff Crank [17] and Bentley Rayburn [18] are gunning for Rep. Doug Lanborn [19], who was first elected in 2006. Lanborn captured the GOP nomination that year by defeating Crank and Rayburn, so tomorrow’s election is a rematch that will decide the favorite in November’s general election.

In the 6th Congressional district, an open seat has again drawn a large field of challengers. Wil Armstrong [20], Mike Coffman [21], Ted Harvey [22] and Steve Ward [23] each hope to replace Rep. Tom Tancredo [24] in the House.

In Nevada [7], there are primary races in all three congressional districts. The contenders in the 3rd CD, Rep. Jon Porter [25] (R) and Democratic challenger Dina Titus [26], should cruise to easy victories Tuesday. In the 1st district, seven Republicans are trying for a spot on the November ballot: Chris Dyer [27], Eve Ellingwood [28], Ed Hamilton [29], Ray Kornfeld [30], Russ Mickelsen [31], Mike Powers [32] and Kenneth Wegner [33].

Rep. Dean Heller [8] in Nevada's 2nd district has found himself in a primary battle with James Smack [34], an outspoken critic of the Republican party and a supporter of Ron Paul [35], a former presidential candidate. Earlier this year, Paul’s supporters in the Silver State forced the GOP to abandon its state convention. While Heller is trying to make small-potatoes of Smack’s candidacy, he probably shouldn’t underestimate Smack’s supporters. The winner will face Jill Derby [36] come November.

As part of our Wiki the Vote [37] project, our citizen-editors have been tallying all the races and building profiles of many of the candidates. We’ll have more on the winners Wednesday (including job descriptions for challengers), so stay tuned then. In the meantime, if you know something about any of the races listed above, or any race in the country, we want to hear from you. Log in to our Wiki the Vote [37] project, find your state, and upload some information about a candidate or incumbent there. It’s easy, and you can always ask one of our staff editors for help.