Wabco Holdings 2012 has been a stellar year for shareholders in Wabco Holdings ( WBC) -- shares of the mid-cap truck part maker have rallied close to 40% since the first trading day of January. But that huge price appreciation may be far from over. Warren Buffett bought shares of WBC with both hands in the most recent quarter, picking up 1.6 million shares for a $92 million stake in the firm. The new buy gives Berkshire Hathaway 2.5% ownership of the Piscataway, New Jersey-based firm. Wabco is a key supplier to the commercial truck and bus manufacturing industry, providing critical components like brakes, suspensions, and telematics systems found in around two out of three new commercial vehicles delivered each year. The mission-critical nature of Wabco's systems gives it a defensible moat -- tractor-trailer manufacturers aren't likely to switch brake or clutch control providers on cost alone, particularly if that switch could impact safety or reliability. While Wabco enjoys standard-bearer status as a supplier to the commercial vehicle market, the firm also supplies components for passenger cars. Financially, Wabco is in stellar shape, with more than $225 million in cash on its balance sheet, and zero debt. The firm has been working to pay down its debt for the last several years, so the debt-free status in the most recent quarter should lead to extra value being returned to shareholders now that WBC has considerable excess free cash that its generating each quarter. That's a good reason to give this firm a second look... Media General Wabco isn't the smallest name on Berkshire's buy list right now. That honor goes to Media General ( MEG), a small-cap news media company based in Richmond, Virginia. Buffet bought 4.65 million shares of the media firm, buying 17% of MEG's outstanding shares this past quarter. Buffett is no stranger to Media General either -- Berkshire acquired 63 local newspapers from the company back in May, and extended a $400 million loan to Media General as part of the deal. But Buffett's close connection with the firm has spurred the desire for an even closer one, so the team in Omaha has been buying up shares. Media General's news assets run the gamut, ranging from broadcast TV stations to news websites and mobile sites.