Our investing hero Peter Lynch once said that the best stock may be the one you already own. Students of investing have heard that gem many times before, of course, but that doesn't make it any less true.

In addition to scouring the investing landscape for new ideas, we'll be identifying our favorite existing recommendations from the portfolio each month. Here are the three best buys for May from the 10-Bagger portfolio:

1. Fusion-io
In today's data-driven world, processors that sit idle waste both time and money. Fusion-io (NYSE: FIO) solves that problem by using solid-state memory and proprietary software to make sure server processors are always working.

More and more companies see the benefits of Fusion-io's products, and the company reported 40% revenue growth for its most recent quarter. The market, alas, didn't care for its flat sequential revenue guidance. Fortunately for investors, it's likely that the slowdown is only temporary. Management says there's still considerable demand out there. And the company's latest product, the ioDrive2, is ready to meet it.

Much of that demand comes from the enterprise sector, namely customers like Apple (Nasdaq: AAPL) and Facebook. Together, their revenue contributions grew 8% sequentially. Both customers recognize that high server utilization keeps their users up-to-date.

The bottom line is that the potential market remains large, and the company continues to upgrade its products. We think that will lead to plenty of future growth, making today's stock price attractive for long-term investors.

2. MAKO Surgical
MAKO Surgical (Nasdaq: MAKO) was taken to the woodshed after its recent earnings release. The company missed revenue estimates because some of its system sales did not come to fruition during the quarter. As a result, the company lowered its system sales guidance by four machines out of 60, but maintained its guidance on procedure counts.

Even with the short-term miss, it's important to look at long-term trends. Here's how things have been progressing.

Source: S&P Capital IQ.

With growing systems and procedure sales, the spectacular decline in MAKO's share price is completely disproportionate relative to the company's long-term future. Our aging population will need more and more knee and hip replacement surgeries. And, according to management, MAKO's robots help hospitals meet that demand -- and make money for the hospital in the process. That's what makes MAKO Surgical attractive over the long run.

3. InvenSense
We live in a device-filled world, and InvenSense (NYSE: INVN) helps make those devices more useful. The company makes tiny motion sensors that enable users to interact with their electronic devices dynamically. Swing your Wii hand-controller and you can hit a golf ball down the digital fairway. Move your smartphone and tablet and you can open your favorite app. As its sensors become more and more prevalent, developers will create more and more ways to use them.

Coming out of earnings, the market punished the company. The results appeared solid, but the company tweaked its revenue guidance slightly. The market didn't want to hear that and the stock sold off. We like when markets do irrational things. That's what provides us with opportunities.

There are numerous existing and potential devices that will use these sensors in the future, and InvenSense is the clear leader in producing them. It will look to put sensors in smartphones, tablets, fitness equipment, digital cameras, and anything else it can dream up. Right now, it's the standard for Android-based phones, and it's working with Microsoft (Nasdaq: MSFT) to provide a solution for its Windows 8 release. Investors looking out three years instead of three months will be rewarded at today's prices.

Ultimate success
All three of our best-buy companies have seen their share prices decline considerably over the past couple of weeks. It's been an unpleasant sight to see, and we've taken a closer look at all three businesses to make sure the underlying investing theses haven't changed.

We remain excited by all three of these businesses, and take solace from another quote from Peter Lynch. He once said, "[Your] ultimate success or failure will depend on your ability to ignore the worries long enough to allow your investments to succeed. It isn't the head but the stomach that determines the fate of the stock picker."

Wise words from an investing legend. For additional investing ideas, be sure to follow us on Twitter, @TenBaggers. You can also add each of the best buys now to your very own My Watchlist to get all of the latest coverage.