The market sell-off has been wide-reaching: It has hurt big stocks and small ones, dividend-paying stocks and non-payers, domestic stocks and foreign ones. It has seriously cut down nearly every industry. And if you're anything like me, it has tried your nerves.

But very smart people -- Warren Buffett and Marty Whitman, to name two -- believe now is a good time to be looking to buy good stocks. What industries look undervalued at today's prices? I put that question to three Motley Fool newsletter service analysts. Here's what they had to say:

Joe Magyer, senior analyst: In a market where boring is beautiful, you'd think the shares of energy transfer master limited partnerships (MLPs) would be magnetic. So far, you'd be wrong. Very wrong. Instead of flocking to secure, fat-yielding MLPs to protect their downsides, investors ran for the exits over concerns that tight credit markets would eventually stifle the ability of MLPs to grow their payouts. But, as usual, Mr. Market has overreacted.

First, most MLPs don't even need to expand to grow profits and distributions. Thanks to rising product volumes and high operating leverage, top-tier names like Kinder Morgan Energy Partners (NYSE:KMP) and Enterprise Products Partners (NYSE:EPD) would be able to grow their distributions without dropping another dime on growth initiatives. Second, neither has any sizable debts maturing in the near term, which means the capital crunch will likely fly over their heads. Oh, and did I mention both these names yield above 7%?

Right now, both Kinder Morgan and Enterprise Products are priced for about 1% annual distribution growth. That is -- how should I put this? -- ridiculous. Each currently offers secure, hearty, growing payouts, little downside, and plenty of upside. If you value stability and quarterly dividend checks, this is exactly the industry you need to be looking at.

Mike Olsen, senior analyst: The markets have taken a round swing at anything that pulls natural gas from the ground. Amid declining natural gas prices and concern over these companies' ability to support E&P budgets (and growth) -- as the credit crisis has limited the availability of debt -- these stocks have been shellacked. But I don't worry too much over these factors: they're notably short-term in nature.

My own research, and many other accounts, estimate the marginal cost of natural gas at somewhere between $6-$7 per thousand cubic feet or higher. What does that mean for natural gas prices? A handful of companies stop producing gas at or below the $7 mark, because it's economically unprofitable. That reduces natural gas inventories, and so available supply dwindles and gas prices in turn recover. So unless we legislate cold weather out of existence, I wouldn't expect natural gas prices to stick around $6 for too long. When that snaps, expect E&P shares to recover in a big way.

Concerns also abound over whether these companies will be able to continue to grow, or they'll be able to replace existing reserves amid constrained budgets. Most of these companies require debt to grow. But I think that misses the big picture. Many of the best natural gas E&Ps have many years' worth of reserves on tap. Further, though growth may be constrained, the better operators can pull plenty of gas from the ground with cash from operations.

A secondary consideration: Many of these companies are so cheap that they don't need to grow to justify current valuations. They only need to maintain current production levels, a pretty manageable hurdle. Also remember that this isn't the end of the line. Many will grow, even if not next year -- and they're possessors of some pretty valuable assets. That value should be realized somehow.

These factors have conspired to put some of the sphere's best names on sale: Chesapeake Energy (NYSE:CHK) and Ultra Petroleum (NYSE:UPL), to name two.

Charly Travers, associate advisor, Million Dollar Portfolio: Health-care stocks are dirt cheap right now. I'm particularly fond of two of the 800-pound gorillas: UnitedHealth Group (NYSE:UNH) and Pfizer (NYSE:PFE).

UnitedHealth is the largest health insurer in the United States, and Pfizer is the largest pure-play drug company in the world. High-quality companies like these don't go on sale often, so when they do you need to take a long look.

Investors are shying away because they don't like some of the near-term uncertainty, but in my opinion, the market is pricing these companies like they're going out of business. That's incredibly shortsighted -- these companies are cash cows. They aren't going anywhere. With what I view as UnitedHealth's normalized cash flow, it could buy back all of its shares in about six years and take the company private if it felt like it. That's a cheap stock.

Pfizer, on the other hand, is priced like a drug company in runoff, where the only cash flows it will ever get are from its current drugs between now and when they lose patent protection. The market is essentially saying that Pfizer will never launch another drug again. That's absurd.

These two companies are not recession-proof, but they are recession-resistant. With UnitedHealth and Pfizer, you get fortress balance sheets, and in Pfizer's case a juicy 7.5% dividend yield. These stocks may not go on to be five-baggers, but their owners can sleep well at night, and at these prices, I believe they're undervalued.

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