This has been a summer most investors would like to forget. Commencing around the time of S&P's decision to downgrade the United States' debt rating, the market has gyrated violently and now sits 12% lower than it was on May 1.

Our Rising Stars have been picking stocks for the past 10 months, and they have been jumping on undervalued large-cap stocks along the way. For the purposes of this article, we'll consider "value stocks" to be ones that have a price-to-book value in the bottom 40% of all companies.

Below are five top value picks our Rising Stars made, along with some food for thought about each stock.

Petrobras (NYSE: PBR)
Back in January, Jordan DiPietro tapped this Brazilian energy company for his portfolio. Specifically, Jordan believes that the company has significant access to valuable resources -- both in the Campos and Santos basins of Brazil and in deepwater drilling -- and the expertise to capitalize on those resources.

From a valuation standpoint, there was a lot that Jordan liked, especially about dividends for shareholders. As he put it at the time: "The company pays a nice 3.6% dividend yield (higher than competitor ExxonMobil (NYSE: XOM)) that is easily supported by its 35% payout ratio, and this dividend only stands to increase as the company throws off more and more cash flow from operations." Petrobras remains on Jordan's scorecard, meaning in his opinion, it's a strong buy.

Raytheon (NYSE: RTN)
Anand Chokkavelu picked this defense company, along with a number of others in the industry, back in January. His thesis was very simple: "Defense offers us a chance to buy into an industry that's more stable than the market's pricing. Companies are trading at historically low multiples, and even though the pie may get smaller because of cuts by the U.S. Department of Defense, I'm betting the currently envisioned extent of those cuts is an overreaction."

Since then, however, Congress has decided to use the defense budget as the centerpiece for a game of chicken. The hope is that looming defense cuts will force both sides to come to the table once again to hammer out a long-term debt deal. If the shenanigans go too far this time, Raytheon could be in for a world of hurt.

Having said that, Anand is still holding on to his shares, meaning he still believes in this defense company.

Berkshire Hathaway (NYSE: BRK-B)
Normally, I might say it's simply cliche to include Berkshire, the holding company for the greatest value investor of our time, on our list of top value plays. The fact of the matter, though, is that this company is sitting in the bargain bin right now.

Rising Star Alex Pape bought the company for his portfolio back on Jan. 18, and just this June, Jason Moser jumped at the chance to buy Berkshire on the cheap. In explaining the value that's not being appreciated here, Jason said:

Buffett's proxy of value for Berkshire is book value. From 1994 to 2010, Berkshire traded at an average price-to-book multiple of about 1.8. Today, it's trading for a little more than 1.1 times book value, which gives me reason to believe that today's price is not only fair, but also fairly inexpensive, considering the quality we're getting.

The math whizzes out there will tell you this means that Berkshire is currently undervalued by about 40%!

Transocean (NYSE: RIG)
This infamous offshore driller is best known for its role in the Deepwater Horizon disaster in the Gulf of Mexico last year. Certainly, back in those days -- when the company saw its share price cut in half in just a few short months -- it could easily be considered a deep value play. But these days, shares are trading for only slightly more than they were in the darkest days of 2010.

Rising Star Jim Mueller selected Transocean as the inaugural pick for his "Messed Up Expectations" portfolio, and since then the stock is down 20%. More recently, Michael Olsen hand-picked Transocean on June 29.

Michael was specifically impressed with the company's dominant market position: "Because Transocean owns half of the existing worldwide deepwater and ultra-deepwater fleet, and capital barriers to new builds are substantial -- they cost $300 million to $700 million each -- the company can influence rates and extract attractive terms through disciplined contract negotiations."

Activision Blizzard (Nasdaq: ATVI)
It's not every day that you find a video game company being referred to as a value stock, but Activision is no ordinary gaming company. The Activision side of the business continues to break records with its Call of Duty franchise, while the Blizzard side has a steady stream of revenue coming in from its subscription model. And yet the stock has pretty much moved between $10 and $12.50 since early 2009.

Alex Pape suggested writing covered calls on Activision back in July, while Jason Moser selected Activision as his inaugural portfolio pick in November 2010. Jason pointed to Activision's focus on digital distribution as a key to success: "Activision recognized this trend early on, which is actually what prompted the merger with Vivendi. It saw the success of Vivendi's World of Warcraft subscription-based model and realized the costs and difficulty involved with building such a service."

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