Almost all HTML/XHTML tags have an attribute called: accesskey. What this does is allows the programmer to assign key-codes to elements in the page. For instance, if I did this:

Search: <input type="text" name="Search" value="" access="S" /> 

Then the user could enter: ALT+S to jump to this field no matter where they are on the page. This feature can make a web-site very user friendly. For instance to jump to search field on this page enter: ALT+4.