Voters in 10 states with competitive Senate races have been inundated with more than $106 million in campaign propaganda, an analysis of independent expenditure reports and campaign expenditure records from the Federal Election Commission shows.

The total represents a combination of ad spending by outside groups and candidates' combined, and is likely a considerable understatement as candidate campaign committees' third-quarter filings have yet to be made public by the FEC.

But the spending we know about so far underscores the stakes involved as the two parties battle for control of the Senate, where Democrats currently hold a six-vote edge. Of this year's 33 Senate races, 10 are considered tossups by the nonpartisan Cook Political Report. According to Sunlight's analysis of the publicly available records, those 10 have seen a combined spending of $71 million on media buys.

As of the end of the second quarter, candidate committees in the 10 most competitive Senate contests have spent a total of $35 million on media buys and direct mail to get  their messages to the electorate in the primaries and general election this cycle.

In many states, they're also aided by outside groups that can raise and spend money in unlimited amounts as long as they don't "coordinate" with a candidate: A quarter of the money (nearly $600 million and counting as of this writing) that such groups have spent on the 2012 election has gone to Senate races. Here's a look at some of the races that have seen the most ad buys and that are in the top tier of races attracting money from outside groups, according to Sunlight's Follow the Unlimited Money tracker.

The tracker, which tabulates spending by outside groups, is a more up-to-date barometer of recent spending because while candidate committees only report to the FEC once a quarter, outside groups must register their political expenditures within 48 hours of making them. Figures listed represent spending as of this post. Check here for updates.

Virginia

Outside spending: $17 million and counting

According to Sunlight's Follow the Unlimited Money tracker, the race for the Senate seat that currently belongs to retiring Democrat Jim Webb has drawn the most outside spending so far. The race features two former governors — Democrat Tim Kaine and Republican George Allen (who held the Senate seat before Webb defeated him six years ago) — and has attracted ad buys from big spending super PACs and the Democratic Senatorial Campaign Committee. The GOP-affiliated combine, Crossroads GPS and American Crossroads, has spent about $4 million running ads in the state. The Chamber of Commerce — which like Crossroads GPS,  is not required to disclose donors — spent another $2.7 million. Meanwhile, the pro-Democratic Majority PAC has spent $3.6 million on the race. Majority PAC was founded earlier this year by longtime Democratic two party operatives Jim Jordan and Monica Dixon, and focused on helping Democrats win Senate races; it's donors  include hedge fund manager James Simons and a Nevada based group Working for Working America.

Wisconsin

Outside spending: $15 million and counting

Just a few months after the bitter gubernatorial recall, Wisconsin is now playing host to a close Senate race between Rep. Tammy Baldwin, D-Wis., and the state's former Republican governor, Tommy Thompson for the seat that retiring Democratic Sen. Herb Kohl will vacate at the end of the year. A difficult three-way primary that Thompson finally won depleted the GOP nominee's campaign coffers, so the super PACs have definitely come in handy. Besides the usual suspects — Crossroads GPS, Majority PAC and DSCC — two other super PACs are playing prominently: The American Chemistry Council has spent $648,000 to support Thompson, while the Democratic-affiliated super PAC Women Vote has spent $1.15 million opposing him. 

Nevada

Outside spending: $10 million and counting

The race between former House colleagues Dean Heller, a Republican, and Shelley Berkley, a Democrat, for the Senate seat that Republican John Ensign quit last year over a sex scandal, is drawing considerable interest from some major outside players, including, for Crossroads GPS, the American Future Fund and the U.S. Chamber of Commerce. They're all spending to help Heller, who has the advantage of incumbency, having been appointed to replace Ensign last year by Nevada's Republican governor, Brian Sandoval. Outside groups spending to help Berkley include the DSCC, Patriot Majority PAC, and the American Federation of State, County and Municipal Employees.

Montana

Outside spending: $6 million and counting

It's the clash of the two senatorial party committees in Montana, with the Democratic and Republican senatorial campaign committees each nearing the $2 million mark with spending.  Recent polls show  incumbent Democratic Sen. Jon Tester in an uphill battle, Crossroads GPS and NSCC have spent more than $3.3 million so far against Tester who won by a narrow margin in 2006. Across the aisle, Rep. Dennis Rehberg has seen more than Tester, some $4.8 million spent against him. The two campaigns have also spent about $3.8 million on ad buys this cycle, with Tester recently accusing Rehberg of using offical travel for vacations.

Indiana

Outside spending: $11.9 million and counting

The Indiana Senate race where Democratic Rep. Joe Donnelly has a slight edge as the recent polls show has attracted big contributons not only from the party committees but other outside groups. Crossroads GPS, the Club for Growth and Freedomworks have been spending money to help Richard Mourdock, the state treasurer who upset Sen. Richard Lugar in the Republican primary by arguing that the longtime lawmaker wasn't conservative enough.  Meanwhile the Democratic Senatorial Campaign Committee and the Majority PAC have spent opposing Mourdock. Some of the major donors to the right-leaning super PAC, Club for Growth include venture capitalist Paul Thiel who has given $2 million to the group that supports fiscally conservative policies. 

Other campaigns aren't seeing as much super PAC spending — they have enough of their own money to fund ad campaigns. At the top of the list: The Bay State battle in which Elizabeth Warren is running to oust Sen. Scott Brown, R-Mass., from the seat he won in a 2010 special election after the death of Ted Kennedy, a 47-year Senate veteran and Democrat icon. Warren has been forced to go on the defensive amid  accusations that she had misrepresented herself as having Native American heritage. 

In all, the two have spent nearly $17 million on media-related activities so far, while outside groups have spent only about $1 million in the race. Another example of a contest in which candidate spending trumps that of outside groups: Connecticut, where former World Wrestling Federation executive Linda McMahon has pumped more than $13 million of her own money into the race, according to the Center for Responsive Politics. She's vying with Rep. Chris Murphy, D-Conn., for the seat of retiring Sen. Joe Lieberman, a Democrat-turned-independent. While the candidates had spent a total of $3.5 million on media buys as of the end of the second quarter, the race has seen about $2 million from outside groups.