Large U.S. companies are flush with cash as never before. S&P 500 members hold more than $1 trillion of the stuff, including cash equivalents and short-term investments. That s a 35% increase from the end of 2008.

Why so much? The recent increase is owed to a mix of panic and prudence. A year ago, stock and house prices cratered, consumers clutched their wallets and lenders locked their doors, so company managers responded by selling off inventory and cancelling costly projects. As a result, while paper earnings plunged, cash flow remained relatively healthy, and because most companies stopped buying back shares and a few cut their dividends, cash balances swelled.

There s a longer-term buildup of corporate cash at work, too. Today s stockpile is five times larger than the one companies held 15 years ago. I ve seen several theories on why: it s expensive to repatriate foreign profits, so companies leave them abroad as cash; companies use large cash balances to smooth their stock returns; job-hopping among top executives has led to reduced spending on long-term projects; managers enjoy increased clout when they control a cash war chest; and so on. My own theory is that two decades of serial asset bubbles have simply made stock gains easy, and investors are too busy cheering for higher prices to badger managers about idle cash.

Whatever the reason, cash put to good use can propel stock prices higher. Deutsche Bank recently published a report highlighting S&P 500 members that the investment bank believes will spend sharply more on dividends and share repurchases in coming years, based in part on the portion of cash flow they ve retained of late, and on the amount by which their available cash exceeds their costs. Below are three companies mentioned in the report.

Pfizer

Nearly one-third of Pfizer s estimated sales this year will come from drugs that face patent expirations by 2014. Under even the most optimistic assumptions, new drugs currently in development won t replace all of that. Hence, Pfizer trades at less than eight times this year s earnings forecast. Last year, the company halved its dividend payment to fund its $68 billion acquisition of drug maker Wyeth. So battered is the stock price, though, that what s left of the payment still makes for a giant yield: 4.2%. Pfizer now has more debt than cash, but just the same, it has more cash than it needs, considering its strong cash flow. Investors worst fears and then some may already be reflected in the stock s valuation.

Quanta Services

Quanta Services designs, installs and repairs infrastructure for power, cable, telecom and gas companies. It stands to benefit from the need to upgrade the nation s power grid, from a push for more wind and solar power and from increased demand for fiber-optic communications. The company s sales are forecast to rise 21% this year and its earnings per share are projected to climb 33%, owed mostly to a recent acquisition. Last year, the company spent less than half of its operating cash flow on capital investments, with the rest helping to increase its cash position. Quanta has enough cash on hand now to pay a one-time dividend of more than 13%.

NetApp

NetApp specializes in networked data storage. Its products have long been used by small and midsize companies for backup and disaster recovery needs. Increasingly, they re being used to centralize data storage, eliminate duplicated data and reduce the amount of physical storage that companies must buy. Companies spent stingily on their computer networks last year, but as the economy thaws, they re spending more. Sales for NetApp are expected to increase nearly 16% over the next year, and earnings estimates are on the rise. The company holds cash equal to more than one-quarter of its stock market value.