Already described:

a:link a:visited a:hover a:active

Also available for all elements:

:hover
:focus
:first-child
:lang

• hover is dynamic and applies to the element the cursor is over
• focus is dynamic and applies to the element in focus (input, for example)
• first-child applies to the first-child of a parent
• lang applies to elements in the language specified

div p:firstchild {color:red}

• The first paragraph that is part of a div is coloured red
• Often useful to collapse space between two titles