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The official start of summer is nearly here. While stock markets are generally less active during the warmer months, that doesn't mean that investors should stop searching for the best stocks to buy.

The market may be near all-time highs, but there are still plenty of good deals to be had. We asked five of our Foolish contributors to present their best stock ideas for June. Here's what they had to say.

Dan Caplinger: It's been years since I set foot in a McDonald's (MCD -2.12%), and I can't say that I've missed its food offerings. But from an investing standpoint, the fast-food giant has made big strides, and has regained the confidence of its shareholders with reawakened growth opportunities.

The highest-profile move that McDonald's has made recently is to begin offering a slate of breakfast items on an all-day basis. The decision served a couple of purposes for the fast-food chain, giving customers a different price point for meals at any time of day, and also allowing them to supplement lunch or dinner items with the most-popular traditional breakfast items. Even though the initiative is less than a year old, it has resonated well with McDonald's core customer base, and has promise for further growth.

In addition, McDonald's has focused on being more efficient and boosting customer service. After receiving complaints about the length of time its McCafe beverage service was taking, and its impact on other customers, the fast-food giant worked harder to speed up service times, while still improving on order accuracy.

McDonald's has always been a compelling dividend stock, and its current 3% yield, and 40-year history of annual dividend increases show its commitment to income investors. Add to that solid growth prospects, and it's easy to understand why McDonald's has done so well lately, and has potential for further gains.

Todd Campbell: Clinical-stage vaccine developer Novavax, Inc. (NVAX 9.71%) hasn't said exactly when it will announce phase 3 results for its vaccine for RSV, a virus that's a common cause of infant and elderly hospital admissions, but it has said it will be sometime in the third quarter. Given the uncertainty of the timing of this data and the fact that the addressable patient population for this vaccine is massive, risk-tolerant investors might consider picking up some shares now, rather than waiting.

Currently, there's no approved vaccine for the prevention of RSV. As a result, RSV leads to 132,000 infant hospitalizations, and 180,000 elderly hospitalizations in the U.S. every year. Novavax estimates that 111 million seniors could benefit from an RSV vaccination by 2020. 

Admittedly, there's no guarantee this vaccine's phase 3 trial will succeed, but the vaccine was effective in seniors during its phase 2 trials, and those trials included more than 1,600 people. Because the FDA has already granted Novavax fast-track status for its RSV vaccine, if late-stage results confirm mid-stage results, then Novavax's vaccine could hit the market as soon as 2017.

Undeniably, this is a risky stock that's best suited to those who can withstand a potential phase 3 failure; but given that Novavax's management has said that this could be a multibillion-dollar vaccine, and the company's market cap is only $1.7 billion, it may be worth the risk.

Tim Green: Shares of International Business Machines (IBM -0.03%) have staged a major comeback after slumping to a multi-year low a few months ago. The stock is still down considerably during the past few years, but investor pessimism may have finally bottomed out. IBM's ongoing transformation has been painful for investors, in part due to shifting currency exchange rates that have zapped IBM's revenue and profits. But the company is in far-better shape than many assume.

IBM's growth businesses, which include cloud computing, analytics, security, mobile, and social, have generated $29.8 billion of revenue over the past 12 months, or 37% of IBM's total revenue. Total cloud revenue, which includes hardware, software, and services, has reached a $10.8 billion annual run rate, with half of that total derived from cloud delivered as a service. IBM's focus is on serving enterprise customers and providing high-value cloud services, not trying to be the largest cloud-computing provider.

The legacy portion of IBM's business is shrinking, driving four years of revenue declines. But IBM remains an extremely profitable company with a customer base unlikely to abandon Big Blue. About 80% of IBM's clients use multiple IBM solutions, and despite the negative results over the past few years, IBM still generated $17.7 billion of adjusted pre-tax income during 2015. That's an operating margin of about 21.7%. With the stock trading for about 11 times the low-end of the company's earnings guidance, IBM deserves a look in June.

Brian Feroldi: The S&P 500 may have fully recovered from its abysmal start to the year, but biotech stocks are still deeply in the red. That's creating bargains for opportunistic investors. Because I'm personally excited about Regeneron Pharmaceuticals' (REGN -1.32%) future right now, I think it's a great time to give this company a closer look.

Regeneron's stock has been one of the best-performing stocks over the past decade thanks to the unbelievable success of Eylea, its treatment for wet age-related macular degeneration. Although this drug has been on the market for a few years, management is still expecting Eylea's fast growth to continue, calling for growth of at least 20% in the U.S. this year. If that forecast proves accurate, then sales will likely eclipse $3 billion stateside this year, and roughly $5 billion worldwide.

Elyea's continued growth is reason enough to be excited about Regeneron's future, but the company also has several other potential blockbusters in the making that could really turbo-charge its top line.

Of particular interest to me is Praluent, the company's recently launched drug that is used to lower levels of bad cholesterol in the blood. So far, sales of Praluent have been disappointing; but that could change in a hurry if its ongoing ODYSSEY OUTCOMES study shows that using the drug lowers a patient's risk of having a heart attack or stroke. If it does, then insurers will likely remove many of the roadblocks that are in place right now to restrict access to this drug, and sales could really take off. Investors should have a look at the results from this study in a few quarter's time.

While we wait, Regeneron continues to move two of its other potential blockbusters down the regulatory pathway. Sarilumab, its drug for treating rheumatoid arthritis, is currently in the FDA's hands, and a go/no-go decision is expected by Oct. 30. Dupilumab, the company's potential treatment for eczema and moderate-to-severe atopic dermatitis, should be in regulators' hands by the third quarter. Both of these drugs have performed very well in clinical trials, and could be needle movers if they get the green light. 

Add it all up, and Regeneron has the potential to have four blockbuster drugs on the market by 2018. With shares currently down more than 35% from their 52-week high and trading for around 24 times next year's earnings estimates, this is one stock that I'm excited about.

Matt DiLallo: Oil's rapid rise from the mid-$20s up to $50 a barrel has done wonders for oil producers. Not only are cash flows poised to rise sharply, but so are drilling returns. While that will help the entire sector, few companies have been preparing for this rebound to the same degree as EOG Resources (EOG -1.59%), which is what makes it a top stock to buy.

EOG Resources spent the bulk of the downturn building up an inventory of wells that it can develop when oil prices improve. This has included amassing a large inventory of drilled, uncompleted wells, or DUCs, in addition to separating its remaining drilling inventory into premium and non-premium locations.

As things stand right now, the company is on pace to have 230 DUC wells, which is almost a year's worth of wells, that it can quickly bring online to immediately capture the upside of an improving oil market. Further, it has built up an astonishing inventory of 3,000 premium drilling locations, which is more than a decade's worth of drilling. What's important to note about the company's premium drilling inventory is the fact that these wells not only can generate a 10% rate of return at $30 oil, but can earn returns in excess of 100% when oil exceeds $60 a barrel.

EOG Resources plans to hit the ground running as soon as it's confident that higher oil prices are here to stay. With nearly a year's worth of wells just waiting to be completed, and another decade's worth of high-return drilling inventory yet to tap, EOG Resources has the potential to fuel strong returns in the future.