BatchGeo is a batch geocoding service that allows you to get the latitude and longitudes of addresses held in a spreadsheet.
Batchgeo includes a spreadsheet template so that you can just import your data into the template and then copy and paste it into the BatchGeo geocoder. Once you press 'Map Now' the addresses will be mapped onto Google Maps and you can export the results via kml or copy and past the geocoded results back into your spreadsheet.
BatchGeo will even host your created Google Map for you. If you click the "Save / Print / Share" button you will be sent to the web page where your map is hosted. You can then just copy the URL and post a link to it on your web site.
Aus-emaps Bulk Address Geocoding
This bulk address geocoding tool uses Google Maps' geocoding engine to find the latitude and longitude coordinates from a list of addresses.
This service geocodes your addresses one at a time and requires you to save each geocoded result individually. This means that using this service will be a little slower that BatchGeo but does mean that you can validate that each result is geocoded correctly. If you don't like the positional accuracy of a result you can just drag the map marker to the correct position.