(Fortune Magazine) -- Cracking the fastest-growing list is an achievement: It means a company is serving its customers and taking market share from its competitors. Some of these superstars are riding a wave of cyclical growth -- like the energy companies on this year's list. In other cases they are out ahead of a trend or creating their own. But as a business gets bigger, 25%-plus growth in revenues and earnings becomes nearly impossible to sustain. Successful companies must adjust. That's what distinguishes the following five firms: Not only did they once make the Fastest-Growing list, but they kept going, even when the economy stumbled or their sectors ran into trouble -- or when their own management made mistakes. While they aren't on this year's roster, they are still making strides in their respective industries. Several relied on organic growth; others looked to acquisitions to expand. But they all have managed to mature gracefully.