User-agent: * 
Disallow: /administrator/
Disallow: /cache/
Disallow: /components/
Disallow: /editor/
Disallow: /help/
Disallow: /images/
Disallow: /includes/
Disallow: /language/
Disallow: /mambots/
Disallow: /media/
Disallow: /modules/
Disallow: /templates/
Disallow: /installation/

User-agent: *

/index.php?action=555     # will block any dynamic URL which has this
exact path name.  These type of dynamic URL’s are notorious for
creating duplicate content
User-agent: Googlebot 

/index.php?action=*       # will block Googlebot from crawling or
indexing any dynamic URL similar to this path name, not limited to only
one single path.  The * is a wildcard which tells Googlebot to ignore
all URL’s up to and after the * wildcard.
User-agent: Yahoo! Slurp

/index.php?action=*        # will block Yahoo! Slurp (search bot) from
crawling or indexing any dynamic URL similar to this path name, not
limited to only one single path.  The * is a wildcard which tells
Yahoo! Slurp to ignore all URL’s up to and after the * wildcard.