Data Bars are a new Conditional Formatting feature in Excel 2010 and they add a colored bar to your values.
The length of the data bar represents the value in the cell. A longer bar represents a higher value.
You have a Gradient Fill or a Solid Fill to choose from as well as 6 different pre-determined colors.
If you select the More Rules option then you can select more colors as well as many different values types to format.