Every quarter, many money managers have to disclose what they've bought and sold, via 13F filings. Their latest moves can shine a bright light on smart stock picks.

Today let's look at highly regarded value investor David Einhorn and Greenlight Capital, which he founded. Einhorn's investing success as well as his advocacy of financial transparency and accountability have attracted many fans. Although he isn't afraid to short stocks, he prefers going long, and looks for situations where he feels a stock is mispriced.

The company's reportable stock portfolio totaled $6.4 billion in value as of June 30, 2012. The top three holdings, making up about 28% of the overall portfolio's value, are Apple, Seagate Technology (Nasdaq: STX), and General Motors.

Interesting developments
So what does Greenlight's latest quarterly 13F filing tell us? Here are a few interesting details:

New holdings include Hess and Genworth Financial (NYSE: GNW). Some see energy giant Hess as undervalued. It has been disappointing analysts in several recent quarters with its earnings, but it does hold a lot of potential, particularly in natural gas. Greenlight's new position in insurer Genworth is small, so we'll have to see if it grows by next quarter. The company has been struggling recently, partly due to low interest rates and the lackluster economy and sluggish housing market. It did get a boost, though, back in June, when Boston's Highfields Capital Management reported taking a huge stake in the company. Also promising is Genworth's hint of a recovering mortgage market, as it reported a strong jump in insurance-policy volume.

Among holdings in which Greenlight increased its stake were solid-state storage specialist Seagate Technology and Marvell Technology (Nasdaq: MRVL). Seagate is poised to profit from increasing storage demand from both consumers with PCs and the servers of cloud-computing companies. Input prices can be volatile, though, and it does face competition. Still, it also offers a dividend yield near 4%, which it has aggressively increased lately.

Chip maker Marvell took a 15% hit recently, upon delivering disappointing earnings. It didn't help that it reduced its outlook, citing declining PC sales. Some are hopeful about its partnership with LED specialist Cree to produce a dimmable LED bulb, and Marvell has also been rewarding shareholders by buying back stock.

Greenlight reduced its stake in Best Buy, among others. The big-box electronics retailer's stock has averaged annual losses of about 15% over the past five years. It recently posted depressing second-quarter results, featuring revenue down 3% and profits off by 90%, due to store closings and layoffs. Observers are watching to see if its founder will be able to buy the company, as he's proposed doing.

Finally, Greenlight unloaded several companies, such as Dell, Research In Motion (Nasdaq: RIMM), and Roundy's (Nasdaq: RNDY). Dell has been having trouble inspiring confidence among many investors, suffering from soft PC demand globally, though its services division is growing. Research In Motion is in an even grimmer situation, with its stock down more than 70% over the past year. Its BlackBerry is facing tough competition from competitors, and its entrant in the tablet space has been largely unsuccessful, at least thus far.

Greenlight shed its modest position in supermarket company Roundy's, despite the company's fetching 9% dividend yield. The company has been posting disappointing earnings and has lowered its projections, and carries a lot of debt to boot. The grocery business is a tough one, with generally low profit margins.

We should never blindly copy any investor's moves, no matter how talented the investor. But it can be useful to keep an eye on what smart folks are doing. 13-F forms can be great places to find intriguing candidates for our portfolios.

The Motley Fool's most popular free report offers the inside scoop on one company at the heart of the trillion-dollar mobile revolution. Get the information you need -- claim your free copy now.