This article is part of our Rising Star Portfolios series. Follow all of Alex's trades and musings on Twitter.

I asked three of our investing interns, who are spending their summers immersed in a crash-course on investment and business analysis, to share one stock they recently added to their watch lists. If you're looking for new ideas in today's market, here are three companies worth keeping an eye on.

Elizabeth Moran: Thwarting the data thieves
Maintaining an enterprise network in the information age is a challenging task. In a world of hackers and thieves, the risk of an enterprise-level security breach is higher than ever. The increasing use of business applications -- not to mention other bandwidth-devouring activities, like streaming Netflix at the office -- leaves many businesses pushing the limits of their network capacity. This often means that critical business applications get stuck in a virtual traffic jam, at the expense of productivity.

Network security and optimization expert Blue Coat Systems (Nasdaq: BCSI) offers solutions to these increasingly ubiquitous challenges. Blue Coat's network solutions help businesses protect against cyber threats and keep their most important applications running smoothly. But Bluecoat isn't alone in the network management game; Cisco (Nasdaq: CSCO) and Riverbed Technologies (Nasdaq: RVBD) number among its competitors.

So why do customers continue to choose Blue Coat? Three reasons: Functionality, credibility, and switching costs. This network expert's products are repeatedly named the best in the business, and Blue Coat already serves 88% of the Global Fortune 500 companies. That speaks as much to the company's reputation as to the efficacy of its products. It's expensive, not to mention time-consuming and annoying, to switch network protection systems. Those high switching costs leave Blue Coat's existing customers strongly inclined to come back for additional services in the future.

Already dominant among large companies, Blue Coat is now trying to gain a stronger position in the small enterprise segment. The company's focused on using its Cloud Service to deliver software-as-a-service to smaller customers, a venture it launched earlier this year. This opens up the market for small businesses that lack the resources to install expensive network protection hardware. I'm not counting on the Blue Coat Cloud Service to be as successful as its core business, but it sure would be an added bonus to the company's already compelling position. I'll be watching Blue Coat to see what happens.

Igor Meyerson: A great company in an overlooked country
Most people don't look to South Korea for investments -- which means that investors willing to make the search can find many gems there. This is a high-income developed country, with a GDP ranked 14th in the world according to the World Bank. Even better, it was one of the few developed countries that avoided a recession during the recent financial crisis. That brings me to the stock on my radar: Shinhan Financial Group (NYSE: SHG).

Shinhan is the country's largest banking business by market value, serving approximately 17.8 million customers out of a population of just 48.7 million. In 2007, the bank acquired LG Card, which created a financial powerhouse that commanded 23% of the credit card market. Shinhan now issues more credit cards than anyone else in South Korea.

Its strong competitive position aside, Shinhan is also strongly profitable -- the most profitable, in fact, among South Korean banks. No less interestingly, the company has a diverse set of major investors, ranging from French-based banking giant BNP Paribas to the Saudi Arabian Monetary Agency and the Government of Singapore. It's hard to say whether or not Shinhan is the best South Korean bank, but other foreign companies and governments are definitely taking note of its expansion. That earns Shinhan a spot on my watchlist.

Reza Handley-Namavar: More towers in more places
Cell phone providers incur enormous expenses to build out their networks. Each tower costs millions to build, and telecom companies like AT&T (NYSE: T) and Verizon (NYSE: VZ) have to pay those costs up front, before the towers begin generating revenue from customers. That's where American Tower (NYSE: AMT) comes in. This company builds cell phone towers across the globe, then leases space on them to cell phone service providers.

Because American Tower can lease the use of a single tower to multiple service providers without additional cost, the economics of building the towers is much more favorable for them than it is for telecoms. This scale creates a potent value proposition, because it becomes cheaper for the service providers to lease tower space from American Tower than to build towers themselves.

American Tower's contracts with service providers usually last five or 10 years and are almost always renewed. The company already has contracts for $13.5 billion in non-cancellable contracts revenue signed and sealed, allowing American Tower to sit back and let the cash roll in. Operating Cash Flow topped $1 billion in 2010, up about 65% since 2006.

American Tower uses its cash to expand its business worldwide. It has been growing in many emerging markets such as India, Mexico, and Brazil, where cell phones and data use are just now expanding to the general population. As international carriers build out their networks and data capabilities, American Tower will have many more opportunities to expand its core business. I'll be watching.

This article is part of our Rising Star Portfolios series, where we give some of our most promising stock analysts cold, hard cash to manage on the Fool's behalf. We'd like you to track our performance and benefit from these real-money, real-time free stock picks. See all of our Rising Star analysts (and their portfolios) here. 

Alex does not own shares of any company mentioned. Reza owns shares of AT&T. The Fool owns shares of and has created a bull call spread position on Cisco Systems. Motley Fool newsletter services have recommended buying shares of AT&T, Cisco Systems, American Tower, and Riverbed Technology. Try any of our Foolish newsletter services free for 30 days. We Fools may not all hold the same opinions, but we all believe that considering a diverse range of insights makes us better investors. The Motley Fool has a disclosure policy.