So far this year, 922 CEOs have left their positions as top dogs, according to outplacement company Challenger. In September alone, 108 CEOs took a hike. The reasons for departure are the obvious ones, including retirement, scoring a better gig, and performance-based termination. Not so obvious is how a company will perform in the wake of a CEO's departure.

A recent study by FTI Consulting found that a positive stock reaction on the day the new leader is announced typically resulted in the stock outperforming the market by 19% six months later. When a stock fell on the announcement day, it subsequently underperformed the market by an average of 17% over the following six months.

So while everyone else is busy watching Meg Whitman and Tim Cook, here are five of 2011's newest CEOs who don't get the same exposure but have a chance to make a big difference in their companies and your portfolio.

1. William Brown at Harris (NYSE: HRS) -- The Florida based tech-company poached an executive from United Technologies (NYSE: UTX) for its new CEO. William Brown starts at Harris on Nov. 1, as Howard Lance retires.

Expectations are high for Brown; Harris is a small player in a government contracts/defense industry that has taken its licks this year. While at United Technologies, Brown played a key role in that company's acquisition of Goodrich. In a former role as president of the fire safety and security segment, his division's operating profit tripled in five years. Brown has extensive experience in commercial markets, something that should prove invaluable as Harris looks in that direction for the future.

Harris' stock price rose 3.7% following the announcement.

2. Thomas Stabley at Rex Energy (Nasdaq: REXX) -- Earlier this month, the Pennsylvania oil and gas outfit named current CFO and co-founder Thomas Stabley the new CEO. Stabley replaces Dan Churay, who gave no reason for his departure. Operating in the beloved Marcellus Shale, Rex is a small but successful driller; second-quarter operating revenue rose 85% over last year.

Margins are slim in the natural gas industry right now, and putting a finance guy in charge might not be a bad idea.

Shares were unchanged after the announcement, but have been performing extremely well since August.

3. David Meeker at Genzyme -- This biotech darling focuses on developing treatments for rare genetic diseases. Health-care company Sanofi (NYSE: SNY) is Genzyme's parent company after buying it for $20 billion in February, and Sanofi recently named David Meeker as CEO of the Genzyme unit.

Originally responsible for developing the treatments in Genzyme's current portfolio, Meeker has been at Genzyme since 1994. He is the one to watch, as Sanofi is counting on revenue from Genzyme to ease some of the parent company's burden due to patent expirations, price cuts, and a narrow pipeline of new products.

Sanofi's stock price rose 1% following the announcement.

4. Rory Read at Advanced Micro Devices (NYSE: AMD) -- It took the world's second-largest maker of processors for PCs eight months to replace its CEO, but they found someone with tremendous experience in Rory Read. Read comes to AMD from his COO position at Lenovo, and prior to that, he had an impressive 23-year tenure at IBM.

AMD has seen market share grow 1.6 percentage points to 19.4% in the past year or so, but Intel still owns the space, with nearly 80% market share. Read has his hands full, but should be able to draw on his experience driving profit growth at Lenovo to be successful in this position.

Shares of AMD rose slightly following the announcement.

5. Paul House at Tim Hortons (NYSE: THI) -- The Canadian coffee and sandwich shop cut ties with its former CEO back in March, reportedly over succession issues. Now, of course, they have one, as Chairman Paul House has stepped in to handle the role on an interim basis with no permanent CEO in sight.

Though House is not the permanent choice for CEO, Tim Hortons has been dragging its feet finding a replacement, and House's indefinite appointment can certainly impact the company. Analysts believe the Canadian chain has completely saturated its domestic market and will never amount to anything more without successful U.S. expansion.

Right now, it's up to House to expand wisely in foreign markets. Three hundred stores are slated to roll out in the U.S. over the next three years. The company is picking and choosing core markets in border states Michigan and New York, instead of rolling out a blanket of stores across a region.

Once Tim Hortons names a replacement, keep an eye on whether the stock pops.

Foolish takeaway
Management has a way of making or breaking a stock. Keeping a close eye on new leaders can often give investors the insight they need to make better investing decisions.

Fools interested in five more stock ideas should check out this report from Fool equity analysts: "5 Stocks the Motley Fool Owns -- And You Should Too."

Editor's Note: This article has been updated to clarify AMD's size as the second largest processor company, not chip company.

Fool contributor Aimee Duffy doesn't own shares of the companies mentioned in this article. Check out what she's keeping an eye on by following her on Twitter @TMFDuffy.

Motley Fool newsletter services have recommended buying shares of Tim Hortons. Try any of our Foolish newsletter services free for 30 days. We Fools may not all hold the same opinions, but we all believe that considering a diverse range of insights makes us better investors. The Motley Fool has a disclosure policy.