This script adds a latlng() function to your Google Spreadsheets so you can easily convert addresses into latitudes and longitudes.

gistfile1.js

function latlng(address){
    var response = Maps.newGeocoder().geocode(address);
    if (response.status == "OK"){
        var result = response.results[0];
        return '' + result.geometry.location.lat + ',' + result.geometry.location.lat + '';
    }    
    else{
        return '0,0';
    }    
};