Fortune 40: The best stocks to retire on

• How we picked them
• Last year's Fortune 40

The tough economic climate hasn't chilled this $362 million air conditioning and heating equipment maker. In fact, even though sales slid 2%, AAON posted its highest-ever first quarter earnings: Net income was up 5% over 2008 results, to $6.7 million, thanks to lower material costs and better efficiency.

Those results are impressive considering that roughly half of the company's revenues come from the hard-hit sector of new construction. But the other side of AAON's business -- replacing units in existing buildings -- is holding up well, thanks in part to the federal government's push to make older buildings more energy-efficient. "This is where AAON shines," noted Zacks Investment Research analyst John Simon in a recent report.

--Eugenia Levenson

NEXT: SMALL CAP: Exponent