LONDON -- What a month! We saw Greek elections, eurozone bailouts, banking downgrades, and, to top it all off, a LIBOR-fixing scandal.

When I say the S&P 500 has climbed 4% last month, you are probably surprised. Well, more than half of these gains came in the last day of trading.

Europe has been steering markets on both sides of the pond, and the ongoing eurozone sovereign-debt crisis, coupled with the possibility of other big banks being accused of LIBOR-fixing, is still something to watch out for this month, despite June's last-minute rally.

Even in this volatile and uncertain month, there were some key buying opportunities out there. Here, we look at some of June's ADR stars that not only made strong gains in June, but perhaps offer real value going forward.

Elster Group (NYSE: ELT)
Elster Group
's 44% gain came almost entirely on the back of the mid-June announcement that the U.K.'s engineering turnaround specialist, Melrose, was in talks to acquire the German utility-meter maker in an all-cash deal worth more than $2 billion. Melrose offered $20.50 per share, a 25% premium at the time, which naturally led to a similar bounce in the price after the announcement.

Looking ahead, if the deal does go through, Melrose has a great track record of improving the profitability of companies like this. Elster already has a profit margin of around 10%, which Melrose would almost certainly be able to improve upon. Perhaps even more significantly, much of Elster's revenue (about 60% in 2011) comes from the gas market, which leaves the water and electricity side of the business wide open to improvement.

If the deal goes ahead, it is expected to be completed by the end of July. Watch this space!

National Bank of Greece (NYSE: NBG)
That's right -- the national bank of the worst-performing eurozone country rose about 25% in June. Now, this has to be taken in context: May saw the National Bank of Greece shed half its value, but June started to offer up enough good news -- or, rather, not-so-terrible news.

At the start of the month, everyone was worried about what would happen in the Greek election. It is no exaggeration to say that the results were critical not just to the outlook for Greece, but to the entire eurozone and perhaps even the global economy. People were predicting the end of the world as we know it if the anti-austerity, radical-left Syriza party won the election for a second time. But they didn't. Instead, the center-right New Democracy party was able to win the most votes, and then it managed to form a coalition government. This may be tentative, but it is certainly better than the alternative.

And so the crisis was averted -- for now, at least. Greece looks like it will be sticking to the terms of the bailout agreement and remaining within the eurozone for a little longer. So the question to ask now is: Will July see the share price par the rest of the losses it made in May?

Anheuser-Busch InBev (NYSE: BUD)
Last month Anheuser-Busch InBev, the world's largest beer maker by sales, gained 21% after it announced it was in talks with Mexican company Grupo Modelo about a possible deal to expand its current 50% ownership. If Anheuser-Busch were to acquire the entire remaining 50%, expectations are that it would cost $15 billion.

Now, it is still early days in this deal, but Modelo has a lot to offer Anheuser-Busch InBev going forward. It owns the popular Corona Extra beer, which alone is valued in the neighborhood of $5 billion (according to BrandZ Global Brands ranking). More than this, however, Modelo controls more than half the Mexican beer market, and the country itself is seen by industry analysts as offering large potential. Given the early and uncertain nature of the deal, Anheuser-Busch's share price has really been seeing only modest gains in June, with more potential if and when the deal becomes more solid.

Banco Santander (NYSE: SAN)
Spain's Banco Santander -- the second bank in the list belonging to a eurozone peripheral country -- managed to gain around 17% in June despite a sharp sell-off across the sector at the end of last month.

This came mainly after two independent studies showed that it was one of three Spanish banks -- the others being CaixaBank and BBVA -- that had no additional capital needs. This, in the month where the Spanish government asked the EU for a "non-bailout bailout" for its banking industry that could reach 100 billion euros.

Santander may now be in a decent position to ride out the storm facing much of the industry, particularly in Spain. It is hoping to persuade investors to take scrip dividends for its payout this year, allowing it to hold on to its decent tier-one capital ratio. But there are still great risks, not least the potential for new regulatory legislation coming from the EU over the next few months.

AstraZeneca (NYSE: AZN)
Anglo-Swiss pharmaceutical major AstraZeneca has seen steady gains in June, climbing around 10% in the month as some safe-haven buying helped its share price. But this company has more to offer.

Just last week the company announced it will conserve several hundred million dollars in cash after deferring the breakup of its longstanding partnership with Merck. It has already said that this frees up money for short-term acquisitions and share buybacks, with many looking to the potential of a $4 billion takeover of U.S. diabetes drug specialist Amylin, which it has been considering.

Looking at the fundamentals, it also looks like a good prospect. Astra has a dividend yield of 7.1%, far above the 4.1% health sector average or the 2.7% of the S&P. Its return on equity and its profit margin are all above the industry average, while its price-to-earnings ratio is far below both the health-care and S&P averages -- just 7.5, compared with 49.9 and 16.7, respectively. Put simply, this stock seems to be going cheap, even after the 12% rise it saw in June.

Even Buffett is buying
Despite the ongoing eurozone troubles, June did provide some European winners -- and perhaps some European buying opportunities. Indeed, legendary investor Warren Buffett has recently spent more than $1 billion buying the stock of a prominent European large cap.

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Karl does not own any share mentioned in this article. The Motley Fool has a disclosure policy. We Fools may not all hold the same opinions, but we all believe that considering a diverse range of insights makes us better investors. Try any of our Foolish newsletter services free for 30 days.