For investors, foreign stocks are in. U.S. stocks are out.

Since the start of 2009, U.S. mutual fund investors have committed some $33 billion to international and emerging-market stock funds, while mostly avoiding domestic alternatives, The Wall Street Journal reported recently.

Our own Tim Hanson, co-advisor for Motley Fool Global Gains, attributes this to a doomed dollar and a mature economy. He offers little hope that U.S. issues will outperform foreign up-and-comers such as China Green Agriculture (NYSE: CGA).

I beg to differ. America is home to the richest wealth-creating tech opportunity in a decade: cloud computing.

What's in a cloud?
Go ahead, roll your eyes. Cloud computing sounds like "dot-com" all over again: an overhyped phrase that's attracting too much money, too much attention, and consequently, its fair share of ridicule. Oracle (Nasdaq: ORCL) CEO Larry Ellison was at least half-right when he jokingly referred to cloud computing as "everything that we already do."

He's only half-right. Let's get under the hood and define what cloud computing really is. My favorite definition comes courtesy of the National Institute of Standards and Technology:

Cloud computing is a model for enabling convenient, on-demand network access to a shared pool of configurable computing resources (e.g., networks, servers, storage, applications, and services) that can be rapidly provisioned and released with minimal management effort or service provider interaction.

In short: Cloud computing is a model of computing where most of the heavy work is done on the Web, in "the cloud."

A brief personal anecdote
When I first got into tech as a young PR consultant 15 years ago, I'd go to client meetings where some brainy code developer or hardware engineer would draw a cloud in the middle of explaining how his network-centric technology functioned. (Something like this.)

Red-faced, I'd raise my hand to ask a question, then slowly move my hand to point at the inky cumulus on the whiteboard.

Me: "Um, what's that?"

Client: "The network. Those are the servers and storage arrays and whatnot that our software calls."

Me: "OK." (Scratches head.)

The visual cloud as a network metaphor has been around for as long as I've been following tech. Thus, the phrase "cloud computing" is born of industry-speak, reflecting the idea that the Web is a giant mishmash of interconnected infrastructure gathered to serve "clients" (i.e., PCs, phones, etc.) with computing needs.

America is changing everything, again
Here are 10 of the top cloud-computing companies, as identified by Network World in a smart 2009 overview of the process, related technologies, and the businesses being built to take advantage of it.

1. (Nasdaq: AMZN)
Headquarters: Seattle, United States
In the simplest terms, Amazon Web Services (AWS) is a suite of computing services available on demand. Customers can host databases, rent storage space or create virtual servers for any number of Web-based applications. Twitter is a big customer.

2. AT&T
Headquarters: Dallas, United States
The former Ms. Bell has been operating large data centers -- warehouses filled with servers and supporting equipment -- for many years. More recently, she's created a business called Synaptic Hosting, which is eerily similar to AWS.

3. Enomaly
Headquarters: Toronto, Ontario, Canada
Enomaly's technology ties together distinct data centers with external cloud-computing environments such as AWS. Enomaly's technology also allows IT managers to visually manipulate software that exists in the cloud.

4. Google (Nasdaq: GOOG)
Headquarters: Mountain View, Calif., United States
Rather than supplying back-end services, as Amazon does, The Big G is creating some of the Web's most interesting browser-based software for users like you and me, including Google Docs and Gmail. In the process, it's taking a shot at Mr. Softy's desktop dominance.

5. GoGrid
Headquarters: San Francisco, United States
A division of hosting company ServePath, GoGrid offers hosting services that are somewhat akin to what Amazon offers but with more of a self-service flair. GoGrid's "Exchange" is a medium for its technology partners to resell preconfigured bundles of software and server power that can be switched on like a light.

6. Microsoft (Nasdaq: MSFT)
Headquarters: Redmond, Wash., United States
Google's biggest competitor is not only putting portions of its Office suite online, but also has its own cloud-computing platform called Azure. The goal? Create an environment that makes Windows more relevant, rather than less.

7. NetSuite
Headquarters: San Mateo, Calif., United States
One of the first to offer an entire suite of software for managing business functions, such as manufacturing, inventory, and accounting, through the cloud. Ironically, Oracle's Ellison was an early investor.

8. Rackspace Hosting (NYSE: RAX)
Headquarters: San Antonio, Texas, United States
A premium hosting provider known for its commitment to fanatical customer support, Rackspace is growing by setting aside huge numbers of servers for cloud-computing clients. Think of Rackspace as a high-touch version of AWS.

9. RightScale
Headquarters: Santa Barbara, Calif., United States
IT managers use RightScale's "Cloud Management Platform" to define the number of servers and amount of storage they need to deploy software into a hosted cloud computing environment such as GoGrid. RightScale then pulls the necessary pieces together.

10. (NYSE: CRM)
Headquarters: San Francisco, United States
Arguably the innovator when it comes to cloud computing, and certainly the first to declare the "death of software" as we've known it. Today, serves tens of thousands of customers via a customizable business software platform that exists entirely online.

Why these 10?
Good question. I like this as a comprehensive list, because it covers the four elements of the cloud-computing value chain:

  1. Hosting providers (i.e., Amazon, GoGrid, Rackspace).
  2. Business software (i.e., NetSuite,
  3. Browsers and front-end productivity software (i.e. Google, Microsoft).
  4. Tools (i.e., Enomaly, RightScale).

Yet as thorough as this list is, I'd supplement it with two other American companies from our Motley Fool Rule Breakers scorecard. One delivers as much as 20% of the Web's traffic every day. The other pioneered a technology for compartmentalizing a server's resources, geometrically increasing efficiency.

A free trial to Rule Breakers will get you not only the names of both these companies, but also unfettered access to our entire market-beating portfolio. Click here to get started.

More broadly, be wary of breathless warnings against buying American stocks. Yes, the dollar is in trouble. Yes, our economy has yet to fully recover from the Great Recession. But this is still home to the world's most innovative companies, and the cloud-computing opportunity they're creating is too huge to ignore.

Did you hear? Motley Fool Rule Breakers was the world's 10th-best-performing newsletter portfolio last year, according to Hulbert. Already a member of Rule Breakers? Log in here.

Fool contributor Tim Beyers is a member of the Rule Breakers stock-picking team. He owned shares of Google and Oracle at the time of publication. Google, Rackspace, and are Rule Breakers recommendations. Amazon is a Motley Fool Stock Advisor selection. China Green Agriculture is a Global Gains recommendation. Microsoft is a Motley Fool Inside Value pick. Motley Fool Options has recommended a diagonal call position on Microsoft. The Fool owns shares of China Green Agriculture and Oracle, and has a disclosure policy.