By Congresspedia assistant editor Avelino Maestas [3]

As the presidential primary season draws to an expected close tonight, attention is beginning to shift toward congressional races across the country. Seven states are holding nominating contests for House and Senate seats today: Alabama [4], California [5], Iowa [6], Montana [7], New Jersey [8], New Mexico [9] and South Dakota [10]. Our citizen-journalists have kept Congresspedia’s Wiki-the-Vote [11] project humming with updates to candidate profiles and portal pages for every state, but we welcome your knowledge if you’ve got information that can be added. Here’s a quick guide [12] to getting started.

On to the races: Sen. Barack Obama [13] is favored in both South Dakota and Montana, and Sen. Hillary Clinton [14]'s next move remains unknown. Elsewhere, six Senate seats are up for grabs, and 70 House seats as well, and while many are competitive we thought we would highlight some of the most interesting or important races. Click through for our state-by-state breakdown.

Alabama [4]

One of Alabama’s senators, Jeff Sessions [15] (R) is up for re-election. Several Democrats are vying for the nomination to challenge Sessions in November, including state senator Vivian Figures [16]. The state also has two open seats: Reps. Terry Everett [17] (R) in the 2nd district and Bud Cramer [18] (D) in the 5th are both retiring at the end of the 110th Congress.

California [5]

Neither of the Golden State’s senators are up for election this year, but California’s 53 congressional districts are fertile ground for mining interesting contests. Republican Rep. Duncan Hunter [19]’s presidential bid left his seat open: his son, Duncan D. Hunter [20] is among four Republicans seeking the nomination in the 52nd district. The other open seat is in CD-04, where Rep. John Doolittle [21] (R) is retiring. Doolittle announced his retirement earlier this year; the FBI raided his Virginia home in 2007, making it harder for the party told hold the seat had he stayed in the race.

Iowa [6]

Sen. Tom Harkin [22] should cruise to re-election in Iowa, but the 2nd and 3rd congressional districts provide some competitive primaries today. Rep. Leonard Boswell [23] (D) is fending off a challenger from his left, Ed Fallon [24], in CD-03, while three Republicans hope to win a nomination to take on freshman Rep. Dave Loebsack [25] (D) in the fall.

Montana [7]

As in Iowa, Montana’s Max Baucus [26] is unopposed in the primary, and he’s heavily favored to hold his Senate seat in November. That hasn’t stopped six Republicans from entering the fray in today’s primary. The rest of Montana’s congressional delegation – Reps. John Driscoll [27] (D) and Dennis Rehberg [28] (D) – face light competition.

New Jersey [8]
The Senate race in the Garden State is one of the highlights of today’s primary elections, with incumbent Frank Lautenberg [29] fighting for the Democratic nomination against 1st district Rep. Rob Andrews [30]. Two Republicans, Joseph Pennacchio [31] and Dick Zimmer [32], are vying for the Republican nod. Andrews entry into the race also freed up his House seat, which his is wife, Camille Andrews [33], is now pursuing. In the 7th congressional district, Mike Ferguson [34] (R) is retiring, bringing another state into play for New Jersey voters.

New Mexico [9]

A bitter primary for the Republican Senate nomination is raging in New Mexico between Reps. Steve Pearce [35] and Heather Wilson [36], who represent the state’s 2nd and 1st congressional district, respectively. Sen. Pete Domenici [37] – whose retirement prompted Pearce and Wilson to seek his seat – made a late endorsement for Wilson on Friday. Polling is neck-and-neck in the Land of Enchantment between the two, though both trail the presumptive Democratic nominee, Rep. Tim Udall [38], for the general.

With all three House members running for Senate, congressional candidates have sprung up throughout the Land of Enchantment. Republicans can probably count on keeping Pearce’s seat, and Democrats will likely hold Udall’s 3rd district seat, so focus is shifting to CD-01.

South Dakota [10]

Four Republicans have submitted their names to voters in South Dakota, trying for the nomination to challenge Sen. Tim Johnson [39] (D). He should be safe come November, however, following his recovery from a brain hemorrhage last year.

The state’s at-large representative, Stephanie Herseth Sandlin [40] (D), is unopposed in the primary, as is her opponent, Chris Lien [41] (R).

Stay tuned tomorrow for election results for the congressional races and the presidential primary (including an update on the superdelegate picture).