Investment opportunities can pop up at any time, so investors always need to be prepared. Moving into August is as good a time as any to consider some additions to your portfolio.

We asked five of our Motley Fool contributors to each discuss a stock that's worth adding to your portfolio this month. They came up with Whirlpool (NYSE:WHR), Oceaneering International (NYSE:OII), International Business Machines (NYSE:IBM), iRobot (NASDAQ:IRBT), and Abiomed (NASDAQ:ABMD). Here's what makes these stocks special.

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Buy. Rinse. Repeat.

Sean Williams (Whirlpool): Recently, a handful of brand-name companies that are market-share mavens in their respective industries have taken it on the chin, but none looks cheaper than appliance giant Whirlpool.

Whirlpool's issues are twofold, based on its recently reported second-quarter operating results. First, its U.S. appliance business took a hit as higher raw-material costs for aluminum and steel (as a result of tariffs) forced it to raise its prices, and second, its EMEA segment (Europe, Middle East, and Asia) saw sales decline by 12.3% from the year-ago quarter. Both of these factors coerced management to reduce full-year adjusted EPS guidance to a new midpoint of $14.50 from a previous midpoint of $15.

As I opined recently, there's never a good way to spin an earnings guidance cut, or the company's need to raise its prices in the U.S. as tariffs take their toll. But consumers are far more resilient than Wall Street gives them credit for. Though raising its prices will take a few quarters to adjust to, Whirlpool continues to maintain solid market share in North America, and it remains a well-known brand with consumers.

It's also a company that has the ability to hedge against economic downturns. Despite being a cyclical stock, Whirlpool can take advantage of new home construction (and therefore growing appliance sales) during periods of expansion, while focusing on home remodels during periods of contraction, when construction tends to taper off.

Management has also done a good job of expanding into Asia, which offers substantially better top-line growth prospects than North America. Through a handful of acquisitions, Whirlpool has established its presence in the Pacific, which led to its lone highlight -- a nearly 15% sales increase in Asia -- during the second quarter.

Finally, Whirlpool is cheaper than it's been in a decade. The company's forward price-to-earnings ratio hasn't been below 9 since 2008. And as icing on the cake, it's paying out 3.6% yield, which is nearly double that of the S&P 500.

While I'm not brave enough to call this a bottom in Whirlpool's stock, I will say this: if you purchase Whirlpool stock right now and check back again in five to 10 years, I believe you'd have made a handsome return on your investment.

A recovery on the horizon

Todd Campbell (Oceaneering International): Oceaneering International just reported its second-quarter financials, and five Wall Street analysts have reacted to the report in the past week by increasing their 2019 earnings estimates. I think that's only the beginning of an ongoing shift in sentiment for the company from bad to good.

I picked Oceaneering as my "one stock to buy" in May, because I believe that capital expenditures on offshore projects are finally bottoming out. If I'm right, then utilization -- and eventually, pricing -- will rebound for Oceaneering's remotely operated vehicles (ROVs), which oil companies use to install subsea hardware, inspect pipes and facilities, and do maintenance and repair jobs.

We're already seeing rising demand for these ROVs. The company reported that ROV utilization was 54% in Q2, up from 44% in Q2, and because ROVs delivered more operating days last quarter, Oceaneering's companywide revenue improved 26% sequentially to $479 million.

Oceaneering's recovery could be lumpy, and I could be early in recommending shares. After all, its revenue is still declining on a year-over-year basis, and it's still posting quarterly losses.

Nevertheless, I think a slow recovery is the more likely risk to this company than a retreat to its lows. Management thinks the second half of 2018 will be better than first half of 2018, and interest in offshore projects requiring ROVs should improve if oil prices continue to cooperate. Given that backdrop, adding this one to a portfolio still makes sense to me.

The market is ignoring this comeback

Tim Green (International Business Machines): With three straight quarters of revenue growth under its belt, IBM's multi-year transformation finally has some momentum. Growth is slow -- sales jumped by just 2% in the second quarter, adjusted for currency -- but that's the strongest performance from IBM in years. Declining legacy businesses are still taking a toll on the top line, but the company's growth businesses are picking up the slack.

Despite the return to growth, the market refuses to give IBM credit. The stock is basically flat over the past year, and it's down about 33% since peaking in 2013. Based on the company's guidance for full-year adjusted earnings, the stock sports a price-to-earnings ratio of just 10.5. And thanks to more than 20 years of relentless dividend growth, shares of IBM yield 4.3%.

Beyond valuation and the dividend, what's the reason to invest in this century-old tech giant? The company still has some key competitive advantages, including deep relationships with longtime customers and a broad portfolio of products and services that allows it to sign massive cross-technology deals. A recent Whole of Government agreement with Australia, covering hardware, cloud computing, artificial intelligence, blockchain, cybersecurity, and quantum computing, is a prime example of these advantages at work.

With IBM stock still depressed, August is a great time to pick up some shares. If the company can keep the momentum going, it's hard to see the stock trading at such pessimistic levels forever.

Welcome, our (helpful) robot overlords

Steve Symington (iRobot): Shares of iRobot soared more than 20% in a single day last week, after the home robotics leader delivered far better-than-expected second-quarter earnings and increased its forward guidance. But considering the stock is still down more than 25% over the past year -- largely a consequence of a post-earnings plunge in February after Wall Street balked at its initially conservative full-year outlook -- in I think patient investors still have plenty of time to step in and watch its story unfold.

For perspective, that earlier decline came as iRobot consciously chose to forsake some profits in favor of investing to drive top-line growth.

"This is a moment in time where over the next three years the true winners in the consumer robot industry are going to be determined for the next decade," explained iRobot's founding CEO, Colin Angle, at the time.

Last quarter, not only did iRobot's flagship Roomba line enjoy strong sales driven in part as a featured product for the fourth straight year during Amazon.com's annual Prime Day sale, but sales of its smaller Braava floor-mopping bots -- which I recently said will serve as its next big catalyst for growth -- also soared 50% year over year thanks to international demand.

What's more, iRobot recently doubled the size of its revolving credit facility to $150 million, a move it says will provide added flexibility to implement its global growth strategy. Again, for shareholders willing to buy now before the success of that strategy is more evident, I think iRobot stock still has years of market-beating returns ahead of it.

A fallen angel

Brian Feroldi (Abiomed): Few companies have been as red-hot in recent years as Abiomed. The medical device maker's stock is up more than twelvefold over the past five years alone. That's a truly ridiculous move in such a short period. 

You might be tempted to argue that Wall Street's recent love affair with Abiomed's stock isn't justified, but a look at the numbers suggest that the opposite is true. Abiomed's revenue and net income have grown by 279% and 1,430%, respectively, over the same time frame. Clearly, this business is firing on all cylinders.  

Recent results show that Abiomed's ultra-fast growth rate isn't slowing down anytime soon, either. The company just cranked out revenue and net income growth of 36% and 135%, respectively. The huge numbers were driven by the continued rollout of its Impella temporary heart pump system in the U.S. and by fast growth in international markets such as Germany and Japan. The prosperity enabled management to boost revenue guidance for the full year and reaffirm margins, too.

Yet in spite of the broad-based prosperity and ample growth opportunities ahead, Abiomed's stock has been in freefall over the past month. Shares are down more than 20% from their recent high. The decline appears to be attributable to a slight miss in the recent earnings report after adjusting for the effects of a tax benefit. 

I think this recent dip is providing investors with a rare opportunity to buy into this hyper-growth story at a modest discount. While shares can hardly be called cheap -- the stock is still trading for 72 times next year's earnings estimates -- I think Abiomed is a such a high-quality business that the premium is more than justified. 

John Mackey, CEO of Whole Foods Market, an Amazon subsidiary, is a member of The Motley Fool's board of directors. Brian Feroldi owns shares of Amazon and has the following options: short January 2019 $185 puts on IBM, short January 2019 $180 puts on IBM, long January 2020 $170 calls on IBM, and short January 2020 $170 puts on IBM. Sean Williams has no position in any of the stocks mentioned. Steve Symington owns shares of iRobot. Timothy Green owns shares of IBM. Todd Campbell owns shares of Amazon and Oceaneering International. The Motley Fool owns shares of and recommends Abiomed, Amazon, and iRobot. The Motley Fool recommends Oceaneering International. The Motley Fool has a disclosure policy.