It's getting harder for investors to find bargains as markets bounce along near all-time highs. Yet even as indexes set new records, many individual stocks have taken a beating lately. In fact, a full 80 companies, or nearly one-fifth of all S&P 500 constituents, have dropped by at least 20% over the last 12 months.

Most of these stocks have gotten cheaper for good reasons, but a few stand out as potential deals for long-term investors. Below I'll highlight three discounted stocks that you may want to add to your watch list.

Stocks on sale:

Stock

52-week performance

Discovery Communications

(21%)

TripAdvisor

(25%)

Tiffany

(32%)

12-month returns as of July 19.

1. Discovery Communications

Many TV-centered media stocks are struggling under the weight of a shrinking pool of cable-package subscribers. But few networks have fallen as far as Discovery (DISCK): Shares are down 21%, compared to a 13% drop for Time Warner and a 2% rise for HGTV owner Scripps Networks (SNI).

Image source: Getty Images.

Discovery's latest business trends don't appear to justify that stock price performance gap. Advertising revenue rose by a healthy 7% in the U.S. market last quarter, trailing Scripps' 14% spike but besting Time Warner's 5% growth. Discovery is making solid progress at building up its global viewership base and even managed to boost profitability as ratings ticked lower in its U.S. division.

Sure, those subscriber declines are likely to continue and even speed up in the coming years. But that's why Discovery is investing heavily in digital platforms like Discovery Go and Discovery VR. A new round of cost-cutting, meanwhile, should provide ammunition to amply fund such initiatives. Lower expenses should also make it easier for management to meet its goal of roughly 15% profit growth this year -- not bad for a stock valued at just 15 times earnings.

2. Tiffany

Things haven't gone Tiffany's (TIF) way lately. After a disappointing 2015, in which sales fell 3% and net income declined 4%, the jewelry retailer began fiscal 2016 by taking a hatchet to its top- and bottom-line forecast. CEO Frederic Cumenal and his executive team now see this as the second straight year of falling profits.

Image source: Getty Images.

Tiffany's struggles aren't as monumental as its share price decline would suggest, though. Its high-end product segment is seeing steady demand and increasing average prices, which points to real brand power. In fact, Tiffany trounces rival Blue Nile by booking triple its gross profit margin. That gap might widen further as the online jeweler spends cash expanding out of cyberspace to open more physical showroom locations.

In an important way, Tiffany's luxury status exposes it to slumps like these since management can't simply cut prices without harming the brand. That's the right move for the long-term health of the business, even if it can drive significant stock price declines like the one shareholders are witnessing now.

3. TripAdvisor

TripAdvisor's (TRIP 0.34%) shares have taken a hit for the most transparent of reasons: Sales and profits are falling. Revenue slipped by 5% last quarter as GAAP earnings dove by 57%. That's bad news for a growth stock that's valued at a big premium to the broader market.

These declines aren't due to market share losses or management missteps, though. Instead, they're the consequence of TripAdvisor's strategy to deepen its connection to travelers.

Image source: Getty Images.

Through initiatives like instant hotel booking, TripAdvisor is making the purchase experience seamless on its apps and websites. That shift should improve customer satisfaction while driving higher engagement levels. Over the short term, though, it puts pressure on sales and profit growth. TripAdvisor executives call 2016 a "transition year" and project that results will decline in the first half before growth rates recover in the third and fourth quarters. Investors who believe that forecast have a chance to buy a growing force in online travel that's just scratching the surface of a $500 billion industry -- at a solid discount.

It's healthy to see a large stock price drop as a reason to reexamine your investing thesis and make sure it's still sound. But if you're confident that the catalysts behind the slump are short-term in nature, then you might be looking at an opportunity that just got more compelling.