Closing in on the upcoming party conventions, super PACs appear to have lost some of their steam in attracting the big bucks. The big guns of political ad spending took in $30 million during July, reports filed this week with the Federal Election Commission show. That's $25 million less than the previous month. In all, super PACs have raised $343 million since Jan.1, 2011, the beginning of this campaign cycle.

The top donors include names now familiar as repeat super PAC underwriters, along with a few newbies. Among the eight donors who write seven-figure checks last month are three corporate donors and one left leaning nonprofit.

Leading the pack is Texas real estate tycoon Bob Perry of Perry Homes who gave an impressive $2 million to Restore Our Future in July. That brings his donations to the group supporting GOP presidential candidate Mitt Romney to $7 million, in addition to the $4.5 million he has already contributed to the GOP leaning American Crossroads.  Described as a recluse, Perry has long stood out as a supporter of Republican candidates and right-leaning negative ad juggernauts such as Swift Boat Veterans for Truth, the group that in 2004 ran controversial, but devastatingly effective ads attacking the Vietnam war record of Sen. John Kerry, D-Mass., that year's Democratic presidential nominee.

The three corporate donations have also gone to right-leaning groups, two to American Crossroads and one to Restore Our Future.

Stephens Inc., an investment bank in Little Rock, Ark., contributed $1 million to American Crossroads. That's on top of $250,000 that Stephens gave the Karl Rove-founded super PAC in December.

TRT Holdings, upped its total giving to Crossroads to $2 million, with another $1 million donation in July. The TRT total for Crossroads is actually $4 million if you count contributions from the head of the company, Robert Rowling. 

The less familiar corporate donor on the million-or-more list is the Renco Group. The New York-based company gave $1 million to Restore Our Future. Renco was involved in an environmental battle with the government of Peru last year, prompting them to set up a heavy weight lobbying campaign in Washington to help get them out of the mess. Sunlight's Reporting Group followed this story closely.

The only Democratic-leaning organization among the large donors a is a Las Vegas based super PAC Working for Working Americans which has given to the Majority PAC, the super PAC set up to win back the House for the Democrats. The only high dollar contribution to Priorities USA Action, the super PAC supporting Obama, comes from Mel Heietz, ($1,000,000) a real estate developer from Philadelphia and Jon Stryker, ($750,000) both who are proponents of LGBT rights.

Restore Our Future brought in $7.5 million, down from $20 million the previous month, while Priorities USA totaled $4.72 million down from June's $6.2 million. American Crossroads, however, saw an increase in contributions, bringing in $7 million, compared to $5.2 million in June.

While the major super PACs have been running ads since 2011, post-Labor Day is when they will be looking to go full-steam, trying their best to resonate with the electorate. To learn which outside groups are behind the ads you see and what donors are behind them, keep an eye out for Sunlight Foundation's soon-to-be-launched Political Ad Hawk, a tool that will help anyone with a smart phone identify who is trying to influence your vote. 

Update: Working for Working American's was incorrectly identified as a labor group in an earlier version of this story.