Connecticut 5th Congressional District

This seat, which became open when Democratic incumbent Chris Murphy decided to make a run for the U.S. Senate, has become a magnet for outside money. Ten outside groups have dumped $4.7 million into the race so far. A large part of this is a last-minute spending spree favors Republican Andrew Roraback, leading Democrat Elizabeth Esty in a poll released earlier this month, as reported by Politico.

One big eleventh-hour spender, Bloomberg's Independence USA PAC , is providing $1.1 million to support Roraback.  

Another $1 million came from The Government Integrity Fund Action Network, which offers little clue as to who is behind the money, other than an Ohio address and one donation. New York philanthropist and conservative media entrepreneur Roger Hertog gave the group $10,000 back in June. So far, no information on where the $1 million it has dropped in support of Roraback came from or why an Ohio super PAC is so interested in the Connecticut House race. Read more about the shadowy Government Integrity Fund Action Network here.

Esty is getting some help from the Democratic Congressional Campaign Committee, which has spent $1 million to oppose Roraback.

Florida 2nd Congresssional District

In Florida's conservative Panhandle, freshman Republican Rep. William Southerland is trying to hold onto his seat against Democratic state Sen. Alfred Lawson and, as the election approaches, outside groups have been spending money on both sides. According to the Cook Political Report, the district is leaning Republican, but conservative groups haven't let up with outside spending, and Americans for Tax Reform spent more than $1 million in the past month on ads attacking Lawson. On the other side, the DCCC and House Majority PAC have spent about $1 million dollars collectively in efforts to undermine Southerland and give Lawson a boost.

Florida 10th Congressional District

As in the 2nd Congressional District, this central Florida race features a freshman Republican, the auspiciously named Rep. Daniel Webster, trying to become a second-termer. In this case, Democrat Val Deming, a retired police chief, is given high marks for running an aggressive campaign that has given Webster an unexpectedly strong challenge.  In the last month, however, outside spending in this race has been largely from left-leaning  groups. Of the roughly $4 million that has been spent in this race in October, about $3 million has gone towards either supporting Deming or opposing Webster. Key players in this financial frenzy are Florida Freedom PAC and Workers' Voice , whicho have collectively put about $800,000 towards supporting Deming; In addition the DCCC (with $1.4 million) and Independence USA PAC and House Majority PAC (each with contributions of about $200,000) have targeted Webster with negative ads. The National Rifle Association's Political Victory Fund and Institute for Legislative Action and the National Right to Life's  PAC and Victory Fund are Webster's only notable supporters this past month, with about $300,000 in positive media buys collectively.

Florida 18th Congressional District

As if they needed more money: The toss-up race in this Florida district, which stretches long the Atlantic coast north of Palm Beach, was already the second most expensive House race in the country, according to the Center for for Responsive Politics, thanks to the two-way fundraising power of yet another freshman Republican, brash tea party favorite Allen West.  Now, in the closing weeks, comes a rush of major outside spenders with a total of $16.8 million in additional case. The largest: the Treasure Coast Jobs Coalition, spending $2.4 million to oppose Democratic candidate Patrick Murphy. (Click here for more about the New Jersey physician who is a major donor.) The pro-Democratic House Majority PAC responded with $2.3 million to oppose West — who has a  $17 million warchest of his own.

Illinois 8th Congressional District

Conservative groups are dominating the outside money race in this suburban Chicago district where freshman Republican Rep. Joe Walsh is considered the underdog against Tammy Duckworth, a Black Hawk helicopter pilot who lost both legs and part of one arm in Iraq. She later served as an assistant secretary for veterans affairs in the Obama administration. In recent weeks, however, there's been an onslaught of outside funding to help Walsh hold onto his seat:  Now or Never PAC , bankrolled by Midwestern conservatives, has laid down $2.9 million to oppose Duckworth, and support Walsh. Now or Never PAC gets its largest donation through "Americans for Limited Government" and most of the group's spending has occurred in October. The second biggest push is from the Tea Party-affiliated Freedomworks For America , at $2.1 million; followed by the National Republican Congressional Committee with $445,000.

Illinois 12th Congressional District 

This district, which stretches from the suburbs of St. Louis to cover the southwestern corner of Illinois, has seen a recent influx of outside spending with nearly $5.5 million coming in in the last month. Left as an open seat after Rep Jerry Costello, D-Ill., announced his retirement, it was initially considered a solid win for Democratic candidate Bill Enyart, but the Cook Political Report changed the status in early October to a toss-up race, noting that the unpopularity of President Obama's energy policies in the coal-producing part of the state he used to represent may give Republican candidate Jason Plummer a chance. Conservative groups have poured $2.8 million into the effort to erase Enyart's narrow lead. Crossroads Grassroots Policy Strategies, the NRCC, and the YG Network have each spent half a million on media buys and Americans for Tax Reform and the U.S. Chamber of Commerce have also each contributed just over $400,000 on attack ads. Liberal groups have not been watching idly, however. The DCCC has spent nearly $1.8 million in the last month in media buys, and the House Majority PAC has also spent $500,000 on ads targeting Plummer.