Once you've retired, you may think that you can hang up your investing shoes for good. But these days, your money has to keep growing long after you stop working. At the same time, though, you can't afford to take too much risk with your hard-earned retirement nest egg.

To help you out, we asked four of our Foolish contributors to weigh in with their ideas on stocks that retirees and other conservative investors can use in their portfolios. Here are their suggestions.

Tim Beyers:
In my response aimed at more aggressive investors, I suggested taking a look at companies involved in cloud computing. But if there's a problem with the cloud-computing theme it's that it gets too much hype. Too many companies want to say they offer some form of "cloud" service, if only to catch some of the wave before it crashes into the beaches of history.

This is where the otherwise errant comparisons with the dot-com era of the last decade make sense. Hype always attracts hypesters, and investing in hypesters is a great way to lose wealth. Fast.

To be clear, I'm not referring to legitimate but richly valued first movers such as Riverbed Technology (Nasdaq: RVBD). Rather, I'm referring to second and third movers pushing press releases as a means to muscle their way into markets they want a piece of. Think of Move, which offers online real estate listings. Sure, that's useful but is it a critical shift? Could consumers get by without what Move offers? I think so, yes.

Conservative investors are better off thinking about which companies win regardless of what services are offered on the Web. I've got two good candidates: AT&T (NYSE: T) and Verizon (NYSE: VZ). Both yield more than 5% at current prices. Both have paid dividends consistently. And both should once again return to a practice of regularly raising their payouts after completing needed infrastructure improvements to support the increasing mobile data consumption brought on by cloud computing. They are, in a phrase, the safest way to bet on the Next Big Thing and get paid doing it.

Selena Maranjian:
For many decades, utilities were the classic investments for retirees and those nearing retirement, kicking out dependable dividends. In this era of deregulation, though, there's less predictability and more competition. Still, some utility companies remain excellent candidates for the portfolios of older investors. Consider National Grid (NYSE: NGG).

Unlike many energy companies, it (mostly) doesn't produce power. Instead, it maintains a gas and electricity transmission system and is paid by other utility companies when they use its infrastructure -- which they do, in good or bad economic environments. The company is developing alternative energies as well, having built solar energy plants with panels from Evergreen Solar (Nasdaq: ESLR).

Want a solid dividend? National Grid has a trailing dividend yield of more than 5.5%. And with a five-year average revenue growth rate of 13%, the company is seeing the growth it will need to maintain and grow that payout. Nor does the stock look overvalued, as its price-to-book, price-to-sales, and price-to-cash flow ratios are all below their five-year average levels. And best of all, its operations are split between the U.S. and the U.K., offering some global diversification.

Jacob Roche:
Aflac (NYSE: AFL) is definitely one of my top picks. The insurer has consistently had higher returns on equity than the vaunted Berkshire Hathaway (NYSE: BRK-B) and currently has a P/E of 10.9, well below its historical average, and a dividend yield north of 2%, well above its historical average.

One of the things I like best about Aflac is its leadership. I think my girlfriend is actually jealous of CEO Dan Amos, but it's hard not admire a guy who voluntarily ditches his golden parachute amid a terrible business climate and got a 93% "yes" vote on his compensation after the company adopted say-on-pay rules in 2008.

The major worry is that Aflac isn't exactly the most stable stock on the market. Shares dropped 60% in 2009 after an analyst issued a warning on the company. The stock has since recovered, but its status as Japan's top insurer is putting a damper on things. Reports suggest that most of Aflac's customers avoided heavy losses, and the company doesn't think it will impact earnings very much. This isn't new for management either, having made it through the Kobe earthquake without much loss. I think now is a great opportunity to pick up some shares.

Cindy Johnson:
For a company with an uncanny ability to stay ahead of trends, look no further than IBM (NYSE: IBM). It's currently benefiting from early investments in developing markets, business analytics, cloud computing, and smarter planet initiatives. Think of IBM as the Apple of enterprise computing.

IBM doesn't just have a knack for identifying and solving computing problems for large organizations. The company also does a remarkable job of delivering value to shareholders. Over the last five years, its dividend has more than tripled. That's cash you can live on even if inflation heats up.

From 2005 through 2010, EPS grew at an average annualized rate of 19% ... with an unusually high quality of earnings. Management has a well thought-out plan to grow EPS by at least 11% annualized through 2015 -- and a history of doing even better than planned. IBM also has extensive experience delivering impressive EPS growth with only lackluster revenue growth. That's compelling if the economy muddles along for years, as many experts expect.

The stock is trading at a reasonable P/E ratio around 14 and currently yields 1.5%.

To keep your eye on these five stocks, add them to your watchlist today.

What stocks do you think are the best for young investors saving for retirement over the long haul? Share your thoughts in the comments below!