http://ssd.jpl.nasa.gov/horizons.cgi: Direct link to the HORIZONS web interface. This is a very useful link as, if an ephemeris has previously been generated using the web browser, it will bring up the inputs that were last used.
http://ssd.jpl.nasa.gov/?horizons: HORIZONS web page (web interface link can be found here, in addition to multiple formats for documentation).