In a world where cold hard cash is the lifeblood of political campaigns, fundraising reports offer a quarterly opportunity to check the pulse of the cycle’s most closely watched contests.

From July to September, the most vulnerable Senate incumbents once again socked away huge sums of money in an attempt to inoculate themselves against tough 2010 election challenges.

That group includes Senate Majority Leader Harry Reid (Nev.), who raised more than $2 million, and fellow Democratic Sens. Blanche Lincoln (Ark.) and Arlen Specter (Pa.), who brought in $1.2 million and $1.8 million, respectively. Targeted Republican incumbents who raised more than $1 million include Sens. David Vitter (La.) and Richard Burr (N.C.).

Meanwhile, blue-chip recruits in open-seat Senate races also continued to flex their fundraising muscle in the third quarter.

In Missouri, both Rep. Roy Blunt (R) and Secretary of State Robin Carnahan (D) raised more than $1 million.

In Ohio, former Rep. Rob Portman (R) brought in $1.3 million, which more than doubled the haul of his top Democratic challenger, Lt. Gov. Lee Fisher. Fisher raised $621,000, but he also showed a high burn rate with $503,000 in disbursements for the quarter.

Illinois Treasurer Alexi Giannoulias (D) raised more than $1.1 million, which, although impressive, wasn’t enough to beat Rep. Mark Kirk’s (R) $1.6 million raised.

In New Hampshire’s open-seat race, former state Attorney General Kelly Ayotte (R) outraised Rep. Paul Hodes (D), but the Congressman ended September with more than double her cash on hand.

With almost $2.5 million in receipts, Florida Gov. Charlie Crist led the GOP class in fundraising for the quarter. But less important than Crist’s continued success is the unexpectedly strong showing by former state Speaker Marco Rubio (R), whose $1 million raised showed that his primary challenge is certainly viable.

Kentucky’s open-seat Senate race features two of the most intriguing primaries, one on each side of the political divide. Attorney General Jack Conway continues to prove that he’s the better-funded candidate. He ended the third quarter with about $1.7 million in cash on hand to Lt. Gov. Daniel Mongiardo’s nearly $752,000.

But Kentucky’s Republican primary looks like it’s going to be an equally cash-draining battle.

Anti-tax activist Rand Paul (R) is running to the ideological right of Secretary of State Trey Grayson (R), the establishment choice. Using the same Internet-based fundraising network that helped his father, Rep. Ron Paul (R-Texas), collect gobs of money for his 2008 presidential run, Rand Paul broke the $1 million mark during the third quarter. Grayson raised just $645,000 and ended September with $1.1 million on hand to Paul’s $912,000.

Another fascinating primary is taking place in the race to see who gets to take on Sen. Chris Dodd (D-Conn.).

Dodd — who raised $902,000 in the quarter and had about $2.1 million on hand at the end of September — is in the fight of his political life in 2010, but the Republican nomination is up for grabs. Former Rep. Rob Simmons is viewed as the GOP frontrunner, but World Wrestling Entertainment CEO Linda McMahon is hard to ignore after donating close to $3.5 million of her own money to her campaign. She ended the quarter with about $1.5 million in the bank but is reportedly willing to spend upward of $30 million on her campaign.

Simmons raised $968,000 during the third quarter and had about $1.1 million in the bank. Foley raised $785,000 from July to September and had about $1.2 million in the bank on Sept. 30.

Among other high-profile Senate incumbents, Reid’s $2 million in receipts was down from the $3.3 million he raised during the second quarter. Reid has now raised $12 million total this cycle, and he had $8.7 million in cash on hand as of Sept. 30.

Burr brought in about $1.2 million and reported about $3.5 million in cash on hand. Secretary of State Elaine Marshall (D) raised $178,000 in two weeks after filing for the Senate race, but Democrats seem to be holding out for a bigger fish on their side, namely Rep. Bob Etheridge.

Vitter, whose personal issues have made him more vulnerable in 2010, raised more than $1.2 million for the quarter and pushed his cash on hand total to $3.9 million. His opponent, Rep. Charlie Melancon (D) — who formally entered the Senate race in late August — raised $754,000 for the quarter and had $1.8 million on hand at the end of September.

Other top performers for the quarter included Sen. Charles Schumer (D-N.Y.), one of the safest incumbents of the cycle, who raised just more than $2 million and reported over $16.6 million in the bank.

Byron C. Tau and Christie Williams contributed to this report.