Check out Heather Solomon’s extensive 2010 CSS Reference Chart!
See also: SharePoint 2007 CSS Reference Chart
The following CSS Reference Chart highlights the major styles used in SharePoint Foundation 2010 and SharePoint Server 2010. CSS styles are grouped by area of the page and include the class/ID value, an explanation of how it is used in SharePoint and other related information including a screenshot where appropriate. Code (and file location) for the style statement is included.