In the world of server farms, QTS Realty sows a lot of concrete. The company owns secure office buildings that house data centers -- where companies keep their computer equipment. QTS (which stands for Quality Technology Services) owns and operates 10 data centers across seven states totaling 3.8 million sq. ft. It counts almost 900 corporations and government agencies as customers. Organized as a real estate investment trust (REIT), QTS is exempt from paying federal income tax as long as it makes quarterly distributions to shareholders. It went public in 2013, raising $257 million, which it will use to pay down debt, as well as buy and renovate more data centers.