A very, very simple Google Spreadsheet API. Depends on Zend's API, but provides a drop dead simple interface to it.

sgs.php

<?php
/*
 * A truly trivial API for dealing with Google Spreadsheets. Designed to work 
 * with spreadsheets in 'List Form'. The API is designed with absolute simplicity in mind:
 * you set a number of constants, and call either gs_list("worksheet name") or
 * gs_walk("Worksheet name", 'callback');
 *
 * And that's it.
 */



function sgs_list($ws_name) {
  $data   = array();
  $feed   = sgs_feed($ws_name);
  foreach($feed as $row) {
    $entry = array();
    foreach($row->getCustom() as $c) {
      $entry[$c->getColumnName()] =  $c->getText();
    }
    $data[] = $entry;
  }

  return $data;
}

function sgs_walk($ws_name, $handler) {
  $client = sgs_client();
  $feed   = sgs_feed($ws_name);

  foreach($feed as $row) {
    $entry = array();
    foreach($row->getCustom() as $c) {
      $entry[$c->getColumnName()] =  $c->getText();
    }

    $result = call_user_func($handler, $entry);

    if(is_array($result)) {
      $client->updateRow($row, $result);
    }
  }
}

/* ------------------------------------------------------------------------
 * Private stuff down here. Move along, nothing to see.
 * ------------------------------------------------------------------------
 */

global $_sgs_client;
$_sgs_client = null;

function sgs_client() {
  global $_sgs_client;

  if($_sgs_client != null) {
    return $_sgs_client;
  }

  if(!defined('SGS_USERNAME') || !defined('SGS_PASSWORD') || !defined('SGS_SHEET_ID') || !defined('SGS_ZEND_LOADER')) {
    trigger_error("You must setup the environment before you can use SGS", E_USER_ERROR);
  }

  require_once(SGS_ZEND_LOADER);
  set_include_path(get_include_path() . PATH_SEPARATOR . dirname(SGS_ZEND_LOADER) . '/../');
  Zend_Loader::loadClass('Zend_Http_Client');
  Zend_Loader::loadClass('Zend_Gdata');
  Zend_Loader::loadClass('Zend_Gdata_ClientLogin');
  Zend_Loader::loadClass('Zend_Gdata_Spreadsheets');

  $authService  = Zend_Gdata_Spreadsheets::AUTH_SERVICE_NAME;
  $httpClient   = Zend_Gdata_ClientLogin::getHttpClient(SGS_USERNAME, SGS_PASSWORD, $authService);
  $_sgs_client  = new Zend_Gdata_Spreadsheets($httpClient);

  return $_sgs_client;
}

function sgs_feed($ws_name) {
  $gd_client  = sgs_client();
  $ws_id      = false;
  $ws_query   = new Zend_Gdata_Spreadsheets_DocumentQuery();
  $ws_query->setSpreadsheetKey(SGS_SHEET_ID);
  $ws_feed    = $gd_client->getWorksheetFeed($ws_query);
  foreach($ws_feed->entries as $entry) {
    if($entry->title->text == $ws_name) {
      $ws_url_chunks = explode('/', $entry->id->text);
      $ws_id = $ws_url_chunks[8];
      break;
    }
  }

  if(!$ws_id) {
    trigger_error("No worksheet found named $ws_name.");
    return null;
  }


  $query = new Zend_Gdata_Spreadsheets_ListQuery();
  $query->setSpreadsheetKey(SGS_SHEET_ID);
  $query->setWorksheetId($ws_id);
  return $gd_client->getListFeed($query);  
}



?>