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A grim picture from Fortune's annual report: "America's 500 biggest companies earned $98.9 billion in 2008, down 85 percent from $645.2 billion in profits the previous year." It was the worst performance in the 55-year history of the list. A clear indicator of how bad the year was—three of the companies in the top 10 of the Fortune 500 also happen to appear in the top 10 list of the year's biggest losers. When embattled companies like Ford and GM remain at the top of the Fortune 500 list, you know the economy's bad. In its yearly roundup, Fortune puts Exxon Mobil at the top of its list, dethroning Wal-Mart, which had held the the top earner spot for two years. Apparently, lower gas prices failed to slow down the Texas oil giant, which filed earning of $45.2 billion. However, all the Fortune 500 companies have learned some tough lessons.