It could be the single-most important factor when sizing up a potential investment. After all, if your target company doesn't disclose key data on market share, growth strategies, or product volume, how can you accurately value its shares?

Fortunately, there are companies that routinely go the extra mile, providing investors with insight beyond what's legally required. For a peek at these standout names, read on.

The best of the best
First off, let's be clear that we're talking about voluntary disclosure practices. In other words, what companies disclose-- and how they disclose it--that isn't mandated by SEC regulations. This may at first seem like a small matter, but for the individual investor -- who rarely has access to the same level of industry and supply-chain data as do the institutional big boys -- it can mean the difference between having a basic idea of a company's operations, and a deep understanding of its relevant risks and opportunities.

For 12 years running, consulting shop MZ has ranked participating companies by the quality and level of their disclosure practices, with categories including best investor relations website and best corporate governance policies. Click here if you want to view 2010's rankings before we proceed.

The go-to source
When investors seek one-stop shopping for company information, the most logical place to start is at the investor relations website, where one hopes to find archived presentations, conference-call transcripts, and links to quarterly and annual reports.

Accordingly, to kick off our process of naming names, let's start with the investor relations website winners. Mexican homebuilder Homex won top honors. Among the names you'd likely recognize were PotashCorp (NYSE: POT) (No. 9), General Electric (NYSE: GE) (No. 11), and Microsoft (Nasdaq: MSFT) (No. 13) (notably, U.S.-based companies were completely missing from the top 10).

MZ's ranking criteria in this category include depth and breadth of content as well as simplicity and ease of use. On that note, I'm personally most impressed with fertilizer producer PotashCorp.

By clicking on the company's "Why Invest?," "Markets & Industries," and "Segments" tabs, investors receive an effective, easy-to-follow crash course in industry and company fundamentals. After 15 minutes, even the fertilizer newbie will be able to chat up a neighbor on the difference between nitrogen- and phosphate-based products. Moreover, related links guide investors to a nearly encyclopedic collection of industry data, which is organized into bite-size chunks that include friendly pie charts and flow diagrams.

It's all there
While there appears to be significant overlap among the criteria that MZ uses in its category rankings, the Financial Disclosure winners do warrant attention. In this category, MZ is looking at the extent to which companies disclose non-financial operating information -- which, believe it or not, includes such key metrics as market share and prices -- in addition to the quality and detail of discussion that accompanies the required-by-law income statement and balance sheet data.

Scoring the No. 1 and No. 13 category positions in 2009 and 2010, respectively, transportation and business-services goliath FedEx (NYSE: FDX) is a model example. Regarding the company's financial reports, MZ has praised

the quality of the information available in the reports, which contain good insights into the company's operations globally including detailed operating statistics, good information on operating costs and breakdown of operating results per business segment.

Indeed, a quick scan of the company's Q3FY10 Statistical Book -- where investors can find such data points as average daily freight and package volume by quarter -- supports MZ's assessment.

On the other hand, take a company such as PepsiCo (NYSE: PEP), which reports North and South American beverage volume as a single statistic. At best, this practice creates the impression that management views these two obviously different consumer markets as one in the same. At worst, it comes across as a thinly veiled attempt to obscure the unique and significant headwinds impacting the U.S. business.

Doing right by shareholders
Finally, I'd be remiss if I didn't mention MZ's corporate governance rankings. The criteria here include executive compensation and Board independence -- topics that my fellow Fools have covered extensively.

In MZ's 2010 roundup, energy companies Royal Dutch Shell and Nexen placed first and third, respectively, and popular tech stocks Infosys and Cisco (Nasdaq: CSCO) made it into the top five. In particular, I'd direct investors to Nexen's executive compensation practices, where base salary has recently represented only 20%-25% of total executive remuneration, with the balance tied to business results and stock performance. That, Fools, is how you align management interests with those of shareholders.

Final considerations
Ultimately, there may be good reason for companies not to disclose certain information about growth strategies or R&D. In such cases, companies will often cite competitive disadvantage -- the downside of tipping off industry rivals, as well as suppliers, ahead of strategic moves. For instance, while rumors always swirl about Apple's (Nasdaq: AAPL) next big thing, you'll likely never find the company announcing development-stage products in advance.

That said, when a company both plays things close to the vest and tends to turn in spotty financial performance, well, it could be time to raise your standards as an investor.

Microsoft is a Motley Fool Inside Value pick. Apple and FedEx are Motley Fool Stock Advisor choices. PepsiCo is a Motley Fool Income Investor recommendation. Try any of our Foolish newsletter services free for 30 days.

Fool contributor Mike Pienciak owns shares of Nexen, but holds no financial interest in any other company mentioned in this article. The Fool has a disclosure policy.