A bear is prowling. That's definitely the case with Nasdaq stocks. The Nasdaq Composite Index is now down nearly 30% below its previous high, more than enough to be in bear territory.

Sure, bear markets can be scary. However, they can also present tremendous opportunities for investors with long-term perspectives. Here are three great stocks to buy that are down 50% or more.

A person looking at a touchscreen tablet displaying a stock chart  trending downward.

Image source: Getty Images.

1. PayPal Holdings

You might think that PayPal Holdings (PYPL 0.33%) is on its deathbed after looking at its stock chart. Shares of the fintech leader have plunged close to 75% below last summer's peak. However, PayPal's underlying business doesn't match up to that grim picture.

Yes, PayPal's revenue growth is slowing. In the first quarter of 2022, the company reported revenue increased by 8% year over year to $6.5 billion. The departure of eBay is a big reason behind the slowdown. Adjusting for eBay, PayPal's revenue jumped 15%. The company also faced a difficult comparison to the prior-year period when revenue soared 38%. 

But even though it's an industry giant, PayPal is still growing faster than the rate of e-commerce adoption. E-commerce remains a tremendous growth opportunity for PayPal over the long run. The company has also rolled out ways to use its products to pay electronically in physical stores. 

PayPal's valuation is more attractive than it's been in years. The stock now trades at a price-to-earnings-to-growth (PEG) ratio of only 1.02. When growth stocks return to favor (which will happen sooner or later), PayPal will almost certainly soar.

2. Align Technology

Align Technology (ALGN -0.80%) stands out as another former high-flyer that has had its wings clipped. Shares of the dental medical device company plummeted more than 60% below its 52-week (and all-time) high.

Much of Align's fall has happened in recent weeks. Shares sank after Align's disappointing first-quarter results in late April. The company missed Wall Street's top- and bottom-line estimates.

Align CEO Joe Hogan acknowledged that the company faces several headwinds. In the Q1 conference call, he pointed to the continued impact of COVID-19 (especially in China), weaker consumer confidence, the repercussions of Russia's invasion of Ukraine, and unfavorable foreign currency exchange rates.

But Align still managed to deliver revenue growth of nearly 9% in Q1 despite these challenges. And the headwinds that it faces are only temporary. Despite impressive growth over the past decade, Align's market share of the overall orthodontic market is still under 10%. Its long-term prospects still appear to be very bright.

3. Novocure

Novocure (NVCR 6.14%) was a huge winner throughout most of the past five years. However, those winning ways hit a brick wall in 2021. Novocure's share price has fallen more than 70% from the highs set last June.

The company's sales growth for its Tumor Treating Fields (TTFields) therapy has slowed considerably. Novocure also felt the impact of an overall sell-off of biotech stocks. But better days could be ahead.

Novocure expects to report results later this year from the pivotal late-stage Lunar study evaluating TTFields in treating non-small cell lung cancer. In 2023, the company should announce results from late-stage studies targeting ovarian cancer and brain metastases. Novocure also anticipates data from its phase 3 study in pancreatic cancer in 2024.

Combined, these late-stage targeted indications represent a potential market that's 14x bigger than Novocure's current market opportunity. There's a good chance that this beaten-down stock will rebound in a huge way over the next couple of years.