With the stock market soaring, some investors are getting nervous about buying in. There are plenty of reasons to be concerned: Valuations of some stocks are sky-high, despite a recession, high unemployment, and a pandemic.

But there are exceptions to every rule. Sometimes, a stock with great growth potential slips through the cracks, and in-the-know investors can pounce. Here are three companies with big growth potential that the market seems to have overlooked.

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Teladoc: Healthcare on the go

Smartphones aren't just phones -- they're like calculators, flashlights, cameras, and computers all rolled into one device that fits in your pocket. And today, thanks to advances in telehealth, they can also function as a health and wellness provider, too.

Telehealth juggernaut Teladoc Health (NYSE:TDOC) is at the forefront of this trend, offering virtual doctor visits ("telemedicine") through its platform. As you might expect, business has been booming during the pandemic, as physicians and insurers have been promoting virtual visits to help stem the spread of COVID-19. In Teladoc's recently completed Q3 2020, such visits were up 208% year over year, resulting in a 109% revenue gain. 

But Teledoc isn't a one-trick pony. It recently completed its acquisition of Livongo Health, an app-based diabetes management platform that hopes to expand to help patients manage other chronic conditions like hypertension. Livongo has invested heavily in artificial intelligence technology that can help provide personalized recommendations for each patient. 

The recent encouraging coronavirus vaccine news sent Teladoc's shares downward, but there's no evidence that virtual visits -- which are cheaper and more convenient for providers, insurers, and patients alike -- are going away anytime soon. Although Teladoc isn't yet profitable, the current share price dip looks like an excellent opportunity to invest in this fast-growing field.

Clean Energy Fuels: A necessary solution

With President-elect Joe Biden's recent win, the market has bid up shares of clean energy stocks. Wall Street clearly believes that government climate policy is going to change and incentives will appear that will benefit the renewable energy industry. However, shares of Clean Energy Fuels (NASDAQ:CLNE) haven't benefited from this trend. 

That's probably because Clean Energy Fuels primarily supplies natural gas-based fuel for semi trucks, and natural gas -- while cleaner-burning than oil-based fuels -- isn't renewable. 

However, one big trend could power Clean Energy Fuels to outperformance: the need to capture greenhouse gases. Transportation isn't the only source of greenhouse gas emissions: landfills, wastewater treatment plants, and especially agriculture -- the proverbial "cow farts" -- release methane into the atmosphere, and methane is a much more powerful greenhouse gas than carbon dioxide. However, burning methane -- the combustible compound in natural gas -- turns it into less-harmful carbon dioxide (and water). Clean Energy Fuels is turning this equation to its advantage with Redeem, a biogas-based fuel.

To manufacture Redeem, Clean Energy Fuels captures methane from dairies, landfills, and other sources, preventing it from being released into the atmosphere. It then refines it into usable truck fuel. Not only does every gallon of Redeem save a gallon of fossil fuel, it also reduces methane emissions, so the fuel is actually carbon-negative instead of carbon-neutral.

We're never going to fully eliminate methane emissions, so recapture and reuse is a necessary part of the energy landscape. Clean Energy Fuels -- now trading near an all-time low -- offers in-the-know investors a great way to invest in clean energy. 

Darling Ingredients: The other kind of recycling

When you hear the word "recycling," you probably think of aluminum cans. Well, Darling Ingredients (NYSE:DAR) is a different kind of recycler, and it could see a big payday in 2021. 

Darling is actually a recycler of scrap animal fats and proteins from sources like restaurant grease traps and deep fryers, bakeries, and slaughterhouses. It refines this material into useful products for the agriculture, food processing, and healthcare industries, among others. When the pandemic hit and many restaurants abruptly closed, Wall Street worried that Darling would take a big hit, but it's been surprisingly resilient, outperforming expectations in the first three quarters of 2020. 

2021 could be even better for Darling, as the company continues to ramp up production of its latest recycled product: fuel. That's right, Darling is actually turning leftover fats into biodiesel through its Diamond Green Diesel joint venture with refiner Valero. The company just announced that its new production facility is running at full capacity, with another major expansion expected to come on line before the end of next year.

Sales of Diamond Green Diesel have been booming, so even with Darling's 68.3% year-to-date share price increase, the company is only trading at 16 times earnings -- near the low end of its historic range. Darling looks like a buy. 

In the know

Conventional wisdom says that the stock market looks overpriced, and that some sectors -- like renewable energy and healthcare -- may be overvalued. However, in-the-know investors can usually find good bargains like Teladoc Health, Clean Energy Fuels, and Darling Ingredients even in overpriced markets. That's why it pays to look beyond the big headlines to find companies with market-beating potential.

This article represents the opinion of the writer, who may disagree with the “official” recommendation position of a Motley Fool premium advisory service. We’re motley! Questioning an investing thesis -- even one of our own -- helps us all think critically about investing and make decisions that help us become smarter, happier, and richer.