Google Drive has an in document javascript API which allows you to do powerful and crazy things like build a web scraper that runs on a timer. When in a google spreadsheet, go to the tools menu and select "script editor".

google_docs_scraper.js

// Fetch and append the current temperature
function fetchAndAppendWeather() {
  var spreadsheet = SpreadsheetApp.getActiveSpreadsheet();
  var sheet = spreadsheet.getActiveSheet();
  
  // All the actual work is done in the top row.
  // We get the link stored in cell A1 (say http://www.wunderground.com/cgi-bin/findweather/getForecast?query=02217 )
    var weatherLink = sheet.getRange("A1").getValue();

  // we set a formula importing a targeted portion of the web page
  // specified by the link we stored in cell A1
  var temperature = sheet.getRange("C1").setFormula("importxml(\""+weatherLink+"\",\"//div[@id='curTemp']/*/span[@class='wx-value']\")");

  // after we have fetched the current temperature
  // insert a new row, where we'll store our new entry
  sheet.insertRowAfter(1);
  // stick the current time and the value of the temperature 
  // we've extracted into our newly created row.
  sheet.getRange("B2").setValue(new Date());
  sheet.getRange("C2").setValue(temperature.getValue());
}

function dummyFunction() {
  // This is a function that doesn't do anything
  // but can demonstrate how triggers are set up
  // under the 'Resources' menu.
}