Every investor wants to buy low and sell high. The stock market has trended upwards recently, ticking all the boxes to start an official bull market -- and now all your favorite stocks are soaring. Surely it must be too late to set up winning investments amid these rising stock prices. Right?

Fortunately, every upswing leaves a few great stocks behind, which opens buying windows for savvy investors. This surge is no different, and there's no shortage of undervalued companies with fantastic business prospects in the long run. Furthermore, the 35% gain the S&P 500 (SNPINDEX: ^GSPC) index has seen since the end of the last bear market in October 2021 is a fine start -- but bull runs tend to last for years and more than double the value of the leading market index. This soaring trend is probably just getting started.

Let me show you some of my favorite bargain-bin picks in today's unbalanced market. You don't want to be left empty-handed when The Trade Desk (TTD 1.67%) and Universal Display (OLED 1.10%) are ready to run again. The two stocks saw their recent price gains overshadowed by even deeper dips in 2021 and 2022, but these companies stand on the threshold of game-changing breakthroughs.

Succeed in adversity, flourish in prosperity

The Trade Desk was founded in 2009, on the heels of the subprime mortgage meltdown. The idea was to help companies make the most of their advertising budgets in a challenging economy. 15 years later, The Trade Desk is a firmly established leader in optimizing online marketing messages, The company provides a platform for buying and managing ad spots across a variety of platforms, with a heavy focus on connected TVs.

The expertise in optimized ad spending makes The Trade Desk the go-to choice in a difficult economy, when budgets are tight and potential consumer interest runs low. As such, the ad-tech company has delivered year-over-year revenue growth of at least 21% throughout the inflation crisis even though the digital ad market struggled through a tough downturn. Many peers saw their sales growth stall or even reverse into a shrinking trend in this period.

And here's the best part. The Trade Desk's competitive advantage should not melt away when the economy gets back on its feet again. Rather, the fiscal discipline and robust client additions of the lean years will translate into sector-leading upticks in a healthier digital advertising market.

"Regardless of what the macro environment is, we're going to be gaining share," said CFO Laura Schenkein in a recent investor conference. "And when there's that upswing when things pick back up, we're just positioning ourselves to gain more of the bigger dollars as they come."

So The Trade Desk has seen solid growth through the inflation crisis and is positioned for even better results in 2024 and beyond. But nobody told Wall Street. The stock gained a fairly modest 47% in the last year, falling just short of making up for the 33% price drop in the previous 52 weeks.

All told, The Trade Desk's shares are down by 1% in two years. Its valuation ratios may look pricey at first glance, but they are quite low from a historical perspective -- and I don't mind paying a premium price for a profitable high-octane growth stock. And that's what The Trade Desk is today. Last year's even lower prices kept the buying window open even wider, but it's not too late to grab this future growth monster at a bargain-bin share price.

The future is bright for OLED screens

Universal Display develops the patented technology behind organic light-emitting diode (OLED) screens. It sells licenses for these power-sipping display elements to screen-building specialists, who in turn sell their OLED products to makers of high-end TV sets, most smartphones on the market these days, and other electronic devices. The company earns a little extra by reselling actual OLED materials manufactured by specialty chemicals giant PPG Industries (NYSE: PPG).

Both license royalties and material sales are based on the total area each screen-building partnerships out, so the shift from small phone displays to much larger TV screens should accelerate Universal Display's revenue and profit growth as OLED TVs take over the mainstream TV market. Don't laugh -- the same thing happened in smartphones over the years, moving OLED screens from the highest-end handsets to broad availability in mid-range devices. I expect another helping of that lucrative market expansion.

The company enjoys several important catalysts right now. For example:

  • Average screen sizes are growing, thanks to more exposure in the big-screen TV sector.
  • The portfolio of revenue-generating materials is about to expand from red and green pixels to the full red, green, and blue spectrum -- plus supporting host materials for each color.
  • End-market device designers are taking wider advantage of OLED's unique qualities such as transparent, roll-up, and foldable screens.
  • Leading customers such as LG Display (NYSE: LPL) and Samsung Display (OTC: SSNL.F) are expanding their OLED manufacturing facilities at breakneck speed, unlocking economies of scale and lower consumer-level prices for OLED-based devices of the future.

Other potential value boosters include new clients in China, more efficient manufacturing processes similar to industrial-scale inkjet printing, adoption of OLED screens in professional systems such as network switches and data center laptops, and the introduction of OLED-based lighting panels. It's honestly hard to keep up with Universal Display's sheer number of business-boosting projects.

But Universal Display's stock isn't getting the investor respect it deserves. Share prices fell 31% over the last three years, driven by weak demand for new phones and OLED television sets in the late-COVID era and the inflation scare that followed.

Like night follows day, that low demand should bounce back in a stronger global economy, helped by the plethora of catalysts discussed above. Furthermore, people should eventually feel a stronger need to upgrade aging phones and TVs from the pre-coronavirus period.

And just like The Trade Desk, Universal Display isn't a value stock in terms of common valuation metrics. Yet, it's worth every penny of that premium price tag thanks to tremendous growth prospects. I call that 31% price drop an open invitation to stock up on Universal Display shares. You're still watching the early days of a game-changing innovator's growth story, and today's opportunistic investment should pay dividends in the decades ahead.