I'm seeking out socially responsible companies to buy for the real-money Rising Star portfolio I'm managing for Fool.com. The universe of companies with serious corporate social responsibility components may be bigger than we all realize; Foolish community members are helping explore that universe by providing some great ideas on the portfolio's dedicated discussion board.

Here are three that have recently piqued my interest -- and have become serious watchlist stocks.

Sustainability: Just do it
Nike's (NYSE: NKE) come a long way since it caught a lot of heat for sweatshop conditions at some of its factories in the '90s. It's actually positioning itself to be a leader in sustainability; according to Nike CEO Mark Parker, "Sustainability is our generation's defining issue." Not only has Nike pledged to address Greenpeace's push for consumer-facing companies to detox operations, it's also moving to openly publish its sustainability data.

Nike has participated in creating a system for sharing sustainability oriented innovation called GreenXchange, and it's also a founding member of Business for Innovative Climate & Energy Policy, which also includes companies such as Levi Strauss, Starbucks (Nasdaq: SBUX), and Sun Microsystems. Even more interesting, in September, Nike formed a venture capital firm, the Sustainable Business & Innovation Lab, which will back start-ups that dream up alternative energy or more efficient manufacturing methods.

Nike currently trades at 16 times forward earnings and sports a PEG ratio of 1.66. That doesn't look like much of a bargain stock compared to industry peers, unless you want to compare its multiples to those of pricy stocks that aren't quite apples-to-apples comparisons, such as Under Armour (NYSE: UA) or Deckers (Nasdaq: DECK). Nike's trailing annual dividend yield is 1.3%. (Thanks for the heads-up, TripleEFocus1.)

A hearty appetite for social responsibility
Darden Restaurants (NYSE: DRI) is the name behind chain restaurant companies like Olive Garden, Red Lobster, LongHorn Steakhouse, and Capital Grille. Would you believe it's dishing out copious helpings of green initiatives, too?

Darden is putting 1.1 megawatts of solar panels on its headquarters' roof, boasting the largest private solar array in its home state of Florida. Solar energy will subsidize 15% to 20% of its restaurant support center's annual usage; that output amount will equal the impact created if the company's support center went "off the grid" for two months.

In addition, Darden is involved in fishery improvement projects to rebuild ailing fisheries; initial projects focus on the Gulf of Mexico. Other partners include Publix Super Markets and Sustainable Fisheries Partnership. Darden's one of the world's largest seafood buyers, so its actions can have a major positive effect on areas plagued by overfishing, negative environmental impact, and so forth.

Darden's forward price-to-earnings ratio is 11, and its PEG ratio is just 0.98, so it appears to be an appetizingly cheap stock on top of its laudable socially responsible traits. And here's dessert: Its trailing annual dividend yield is 3.2%. (Thanks for the heads-up, DCWD40!)

Green building blocks
Quanex Building Products (NYSE: NX) isn't exactly a household name, even though it's built for greener households. Although I would normally steer clear of companies linked to housing construction in today's market, Quanex offers a forward-looking spin: It provides sustainable building materials and energy-efficient products for the residential construction market.

At a recent glass industry trade show, Quanex President and CEO David Petratis offered heartening insights into the future of the industry: "We are in the worst economic market maybe of my lifetime ... [but] there is more change and innovation going on today than there ever has been in the history of the planet."

Quanex is focusing on emerging innovations in energy efficiency; one example is the acquisition of polymer technology that allows glass to adjust its tint according to ambient temperature.

Is it reasonably priced, though? Its forward P/E is 21, and its PEG ratio is 1.9; the consensus analyst estimate that it could rake in 27.8% growth next year may mean it's cheaper than it looks, particularly given the fact that its business could be more growth-oriented than we know if green building picks up momentum. Bear in mind that Quanex also boasts a trailing annual dividend yield of 1.1%. (Thanks for the heads-up, blesto!)

Picking favorites
Darden looks like the biggest bargain, but we can't ignore the challenges it faces. The restaurant industry has its work cut out for it in today's economic tough times. Dining out is one of the easiest expenses consumers can cut from constrained budgets.

Quanex's futuristic approach to residential building products could ultimately prove the current price quite reasonable given future growth potential. Of course, this depends on an increasing number of people embracing greener, more energy-efficient homes.

Nike is an evergreen-type stock with a strong, pretty bulletproof brand; it ranked No. 25 on Interbrand's list of top global brands in 2011. Nike doesn't strike me as terribly overpriced or a raging cheap bargain stock; however, it might also be the most defensive pick of the three given its strong pull with consumers.

What do you think? Add these stocks to your watchlist, or give your opinion of which is the most promising stock in the poll below.

Alyce Lomax owns shares of Starbucks in her personal portfolio. The Motley Fool owns shares of Under Armour and Starbucks. Motley Fool newsletter services have recommended buying shares of Under Armour, Deckers Outdoor, Starbucks, and Nike, as well as creating a diagonal call position in Nike and a bear put spread position in Deckers Outdoor. 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.