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Shareholders of these stocks had many reasons to celebrate in 2015.

This year has been as ho-hum as you can imagine. The S&P 500 is down by less than 1% -- which isn't bad, considering the index fell more than 11% in the course of just a few days in August. But altogether, 2015 has been pretty unspectacular.

However, a select few companies have seen their stocks skyrocket. I'm not talking about uber-small caps, which can often double overnight. And I'm not going to cover some of the most well-known "doublers" of the year like Amazon.com or Netflix.

Instead, I'm talking about stocks that were worth at least $1 billion at the beginning of 2015, and have seen their shares more than double year-to-date (as of the market close on Dec. 10) but probably aren't on most investors' radars.

Ctrip.com -- Up 122%

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Ctrip.com's English language homepage. Source: Ctrip.com

The year began with Ctrip's (NASDAQ:CTRP) co-founder and CEO James Liang warning that a price war in China's online travel space was going to continue for a few years, and that it would negatively affect the company's bottom line. Since then, though, just about everything has gone Ctrip's way.

Revenue for both its travel and accommodations segments grew more than 40%. More importantly, however, margins steadily improved as the year progressed, showing that Liang's prediction may have been too cautious.

But the real coups occurred when the company decided that rather than competing against some of the industry's largest players, it would join forces with them, inking a merger deal with rival Chinese OTA Qunar, and deepening its partnerships with international juggernauts like Priceline.

Dycom Industries -- Up 131%

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Dycom's bread and butter is in fiber contracts. Source: Kenny Holston, via Flickr.

Here's a company you've probably never heard of before. Dycom (NYSE:DY) is a $3 billion enterprise that's found itself in the sweetest of sweet spots: providing contracting services to help increase the bandwidth for some of the nation's largest telecommunication companies.

As voice, data, and video streaming takes up more and more of the Internet's capacity, telecom giants like AT&T, CenturyLink, Comcast, and Verizon have contracted out the buildup of their respective infrastructures to Dycom. Specifically, its deployment of fiber technologies has been in high demand: Revenue has increased 20%, while earnings have jumped 153% over the past year.

Investors should be cautious, though: The four telecom giants mentioned above account for 56% of Dycom's revenue. If any one of these companies finds a cheaper and equally effective alternative, shares could plunge in short order.

Anacor Pharmaceuticals-- Up 263%

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Photo: Anacor Pharmaceuticals

As the picture above would have you believe, Anacor (NASDAQ:ANAC) is a pharmaceutical company focused on creating boron-based drug treatments.

The company had already been experiencing a great year at the beginning of July -- shares were up 150% by then -- based on the success of its Kerydin treatment for toenail fungus that the company had licensed out to Novartis' (NYSE: NVS) Sandoz unit.

But the potential for a new blockbuster drug got investors even more excited. During July, Anacor released positive phase 3 trials for crisaborole--a topical drug that treats eczema.

Nearly 25 million Americans are affected by eczema, and the company believes that crisaborole could become the primary form of treatment for those patients if the drug is approved. Depending on pricing, it could easily be the company's biggest drug seller to date.

It's worth noting that shares have tempered somewhat since July, as they are down 23% since hitting their all-time highs. Investors looking to make a play on Anacor need to be sure they have enough industry-specific knowledge -- and experience with the swings of pharmaceutical stocks in general--before taking the plunge and buying Anacor.

Brian Stoffel owns shares of Amazon.com,which the Motley Fool also owns shares of and recommends. Mr. Stoffel also owns Ctrip.com International. The Motley Fool owns shares of and recommends Netflix, and Priceline Group. The Motley Fool recommends Ctrip.com International and Verizon Communications. Try any of our Foolish newsletter services free for 30 days. We Fools may not all hold the same opinions, but we all believe that considering a diverse range of insights makes us better investors. The Motley Fool has a disclosure policy.