The summer of 2015 is fading fast, and we're all getting back to work. As September rolls around, it's high time to take another look at your stock portfolio.

A panel of Motley Fool contributors has put together five top-quality stocks worthy of a closer look right now. For the steel-nerved investor, Netflix (NFLX 1.84%) is selling at a deep discount that could grow even steeper at a moment's notice. For Universal Display (OLED 0.87%), several long-awaited end markets for its OLED display and lighting technologies are finally reaching maturity. Biotech titan Gilead Sciences (GILD -1.35%) matches deep value to a fantastic drug development pipeline. Oshkosh (OSK -4.69%) was recently thrown another lifeline by the Department of Defense, and most investors haven't acted on that game-changing development yet. Car-buying innovator TrueCar (TRUE -3.26%) comes off a disappointing report and is looking for a new CEO, but there's plenty of light at the end of that tunnel

That's the bird's-eye view of these top September buying opportunities. For a close-up look, bristling with important detail, just read on:

Source: Universal Display.

Steve Symington (Universal Display): It seems an understatement to say that Universal Display Corporation investors have endured a roller coaster so far in 2015. Though shares of the OLED specialist are still up more than 30% year to date, they're also down more than 30% from a 52-week-high of nearly $56 per share set in June.

For that, investors can thank a combination of the recent broader market pullback and weaker-than-expected second-quarter results announced at the beginning of August. Those results notably included a surprise net loss of $11.8 million, driven by a one-time $33 million writedown of OLED host material inventory and associated work-in-process.

As I pointed out in my full earnings take, however, Universal Display management explained that this writedown was the result of massive new OLED product introductions that utilize Universal Display's new red and green emitter materials, which its customers are required to purchase given the scope of UDC's patents. In turn, this negatively affected demand for older products that used its existing host materials, which customers aren't obligated to buy from UDC.

But over the long term, the influence of Universal Display's host business should wane as its phosphorescent OLED emitters continue to permeate the market. Universal Display's tech notably won a spot via LG Display (its second-largest customer) in the Apple Watch, for example, and supply chain sources suggest the folks in Cupertino could be planning a complete transition to OLED iPhones and iPads in the coming years.

In addition, less than two weeks ago LGD announced it will invest $8.5 billion to expand OLED production over the next three years for OLED televisions, smartphones, wearables, automobile displays, and even rollable and foldable OLED devices. For Universal Display investors willing to patiently watch this growth story unfold, the future looks brighter than ever.

Source: Netflix.

Anders Bylund (Netflix): If you want a brutally volatile stock in your portfolio, Netflix should be right up your alley. I mean that in the best way, since most of the digital video veteran's wild swings go upward, but it's always best to be prepared for ridiculous share price drops as well. Read on for the upside of that terrifying idea.

Riding high on a fantastic second-quarter report and the imminent entry into the Japanese market, Netflix shares were hitting all-time highs on a regular basis in early August. Then the stock lost 16% in the span of a single week. That's $8 billion of market cap value shaved off, for no particular reason other than general market jitters.

That's the downside of volatility: Sometimes these stocks get caught in a downdraft. Since Netflix stock looks expensive by traditional value metrics, any hint of market weakness makes investors sell it and "run to safety."

Now, Netflix quickly repaired some of that mid-August damage. The market had a good day in general, so Netflix swung up faster than your average stock. The company also announced a new partnership that should accelerate Netflix's streaming video growth in Japan.

As I'm writing this, Netflix shares still trade more than 10% below those early August all-time highs. That's a fine discount on this long-term growth machine, which should finish its high-octane growth phase and convert into a high-margin cash generator by 2017.

There's also a very good chance that Netflix shares will drop again in September, for no better reason than butterflies coughing in China. Keep an eye open for baseless price plunges, ready to strike an even better bargain like the one you saw on Aug. 24.

The Pentagon picked Oshkosh's L-ATV to become its new Joint Light Tactical Vehicle. Photo: Oshkosh.

Rich Smith (Oshkosh): I don't know whether Oshkosh will be the best-performing stock in the world in the month of September, but I've got a strong hunch about the next six months.

As you may (or may not) have heard, late last month the U.S. Department of Defense chose Oshkosh as the winner of its multiparty, multiyear contest to build a replacement for the venerable HMMWV (Humvee) jeep. This contract is a big deal for Oshkosh, and potentially transformative. The Washington Post reports the initial contract is for $6.7 billion for 17,000 vehicles and that it could be worth $30 billion or more over time as more than 55,000 of the Joint Light Tactical Vehicles are built for the military.

Up until this contract was announced, Oshkosh as a business was on the ropes. Contracts for its MRAP armored vehicles were drying up, and military spending in general was trending down. Oshkosh still labored under a near-$1 billion debt load, and things were not looking good.

But here's the thing: Oshkosh has been here before. In similar straits back in the summer of 2009, Oshkosh was awarded the contract to build the Army's M-ATV vehicle (a small, all-terrain MRAP). That contract not only threw Oshkosh a lifeline, but sparked a six-month surge in Oshkosh stock that saw the shares more than triple in value.

Will that happen again, this time, with the JLTV contract? I honestly don't know. Last time around, Oshkosh's share surge was turbocharged by the award of a second multimillion-dollar contract (just two months after the M-ATV award) to build a family of Medium Tactical Vehicles for the Army as well. There may be no such double-whammy this year.

But with Oshkosh shares selling today for less than 13 times trailing earnings, paying a 1.8% dividend yield, and expected to post 15% annual earnings growth over the next five years, the shares were looking cheap even before the JLTV award was announced. With that win, I think Oshkosh stock looks even cheaper today -- and a great stock to buy in September.

Brand new Hepatitis C treatment Harvoni. Source: Gilead Sciences.

Brian Feroldi (Gilead Sciences): When the markets become volatile, I like to go bargain hunting for the strongest businesses that I can find. I think the market is giving us quite a deal right now on shares of biotech giant Gilead Sciences, making it my top choice for new money in September.

Gilead currently holds powerhouse positions in fighting two diseases, HIV/AIDS and hepatitis C, with a slew of best-selling drugs that are creating huge growth numbers. Thanks in large part to recently launched hepatitis C treatments Sovaldi and Harvoni, Gilead rang up more than $8.2 billion of revenue in the second quarter alone, up a strong 26% over the year-ago period. This strong growth has given its management team enough confidence to raise its revenue guidance for the second time this year, and the company now expects 2015 revenue to be north of $29 billion.

Gilead isn't resting in its laurels either, as it currently boasts 10 new compounds that are either pending regulatory approval or in phase clinical 3 trials, giving it one of the strongest pipelines in the industry. While some of these new compounds are designed to expand its leadership position in its core markets, the company is also looking to enter new disease states like hematology/oncology and cardiovascular disease.

While we wait to see if any of these new drugs will work out, Gilead is using its financial might to reward investors with a recently authorized dividend payment that currently yields 1.6% and a massive $15 billion share repurchase program. Investors at today's prices are getting all of this for a stock that's trading at just over nine times 2016 earnings estimates.

Growth, value, and income? Count me in.

Source: TrueCar.

John Rosevear (TrueCar): Shares of car-buying service TrueCar were crushed after a disappointing second-quarter earnings miss, dropping over 40%. They haven't recovered -- yet. But the company remains the best-positioned player in a market space ripe for disruption, with a still-strong management team. The earnings miss creates an intriguing buying opportunity.

Simply put, TrueCar partners with new-car dealers and uses the data it gathers from sales to provide transparent pricing to prospective car buyers, which it then connects with the dealers. Dealers get a steady stream of buyers via the company's online service and mobile apps, and buyers get great data and -- ideally -- a lower-stress car-shopping experience.

The company is currently seeking a new CEO; founder Scott Painter agreed to give up the role after the company's poor second-quarter showing. But that new CEO will have a strong veteran team in place: John Krafcik (president) was the former chief of Hyundai North America, Larry Dominique (executive vice president) ran product planning for Nissan's Western Hemisphere operations, and CFO Michael Guthrie has decades of experience in venture capital and technology companies.

TrueCar isn't without risks. Its relationships with dealers have often been rocky, with mistrust on both sides. But it still expects to generate over $250 million in revenue this year, with sales and market share growing. At current prices, TrueCar shares could look like a steal a year from now.