One of the most fertile areas for investment research can always be found among stocks that trade for less than the price of a deluxe cheeseburger.

When a stock is below $5 or $6, many mutual funds are prevented from owning them. Yet if these stocks can make some headway and move up toward the $10 mark, then the stocks will begin to pop up on fund managers’ radars. And when they begin to pour money into these stocks, their buying efforts can quickly move shares up into the low teens.

With that in mind, I wanted to take a fresh look at my favorite names that are trading below $6. That’s not to say that these stocks are micro-caps or nano-caps — I tend to like companies that are worth at least $250 million, as they have to be at least that large to ever get noticed by those stock-moving fund managers. Here’s a quick synopsis of my current favorite stocks under $6.

JetBlue (Nasdaq: JBLU)
This low-cost airline is gradually morphing from industry upstart status into maturity. Gone are the days of white-hot growth, but JetBlue is quietly becoming a profit machine. Per share profits are likely to double this year, and as long as the economy stays aloft, per-share profits should rise another +50% in 2011 to around $0.60.

That profit surge comes even as revenue growth is expected to slow to around +10% next year. I always like to see profits growing faster than sales, as it means that a company is able to squeeze more profits out of each incremental dollar of sales. For JetBlue, the operating leverage comes from continually optimizing its route structure to re-direct empty planes to cities where demand is more robust.

In the most recent quarter, JetBlue flew +5.5% more passenger miles than a year ago, but the number of customers grew nearly +9%. Whereas planes were 79.5% full a year ago, they’re now 82% full. The extra revenue from those additional customers is pure gravy, as the flight attendants, pilots and fuel costs need to be spent whether a plane is half-full or completely full.

Even as JetBlue reaches maturity, it still has more paths to growth. The carrier has nearly $1 billion in unrestricted cash and may look to keep expanding. In recent years, the company has focused on expansion into the Caribbean and Latin America. Those routes have historically been very profitable for the larger carriers such as AMR (NYSE: AMR) and Continental (NYSE: CAL). Further inroads into these areas from JetBlue’s New York and Orlando hubs could help the top and bottom line keep expanding for some time to come.

Leapfrog (NYSE: LF)
I continue to think that this maker of educational toys is emerging as a great turnaround play. I wrote about Leapfrog in July and since then, the company modestly exceeded second-quarter forecasts. [Read: The Best Idea of the Week]

But this is really a seasonal play as the company derives almost all of its profits during the holiday shopping season. It’s encouraging that Leapfrog is posting improving results, and shares can move back to the $7 level seen in April if September results are impressive. But the real break-out for this former highflyer wouldn’t come until confidence is increased that the holiday shopping season will be a strong one.

Innerworkings (Nasdaq: INWK)
Speaking of former highflyers, this provider of corporate printing services and marketing supplies has seen its shares fall from $18 back in early 2008 to a recent $5.50. That’s because growth sharply decelerated as clients cut back on many marketing campaigns.

But Innnerworkings is growing once again. Sales rose +20% in the most recent quarter from a year ago, and earnings per share (EPS) is starting to slowly climb quarter after quarter. To help sales rebound, Innerworkings is putting more resources behind a division that handles Business Process Outsourcing (BPO). In a nutshell, BPO allows large enterprises to focus on their core business and devolve non-core functions such as document management, business workflow and other mundane tasks to firms like Innerworkings.

Analysts expect sales to rise +15% both this year and next, but it’s worth noting that Innerworkings has a history of making highly-accretive acquisitions to bolster growth. If the company can pull off a few small deals, growth could exceed +20% next year. Although I don’t see shares returning to those 2008 heights, I still see upside to the $9 to $10 range in the next year as investors once again embrace this company as a nice and steady growth story.

China Security & Surveillance (NYSE: CSR)
It’s fair to wonder what it will take to really get these shares going. China Security is one of the leading suppliers of security gear to companies and governments in China. The company has posted impressive growth, as sales have risen at least +35% in each of the last four years.

After stumbling in the March quarter, China Security posted much stronger results in the most recent quarter. When results came out in late July, the stock rose +16% in one day to more than $6. Less than a month later, investors have already forgotten the name and it is slowly drifting back toward the $5 mark.

But this is still very much a growth story. China Security has begun to sign an increasing number of government contracts, which typically carry gross margins 500 basis points higher than corporate contracts. The spurt in government business is attributable to a “safe-city” program that seeks to deploy banks of video cameras, traffic management systems and emergency response systems in China’s 200 largest cities. The new government contracts have helped push China Security’s backlog for delivery within the next 12 months up to $213 million from $130 million a year ago and should help meet analysts’ sales forecasts in coming quarters.

Meanwhile shares trade for about five times this year’s projected profits. The low multiple is partially due to the fact that the company has often issued fresh rounds of new stock to raise cash. Management insists that the capital-raising efforts are now completed. If China Security can continue to deliver impressive quarters and refrain from diluting stock any more, then shares may finally start to garner a more robust P/E ratio.

Action to Take –> All of these companies are boosting sales and profits, but their shares are far closer to their all-time lows than their all-time highs. A stumbling global economy might keep a lid on these shares for a bit longer, but when the economy rebounds and growth stocks are back in vogue, they could zoom ahead quickly. You may also want to listen to each of the companies’ upcoming conference calls to be assured that management continues to execute on plan.