According to Bloomberg Businessweek, a company's most important asset is it's brand. Though a brand's monetary value is tricky to measure, a well-managed brand can only increase in importance over time. (Conversely, a good reputation can be lost all too quickly.) Businessweek argues that managing a brand goes beyond marketing- it encompasses everything a company does.
For more on managing a brand, check out "Why So Many Companies Get Branding Wrong