Some really common layout classes I use in almost every CSS file.

/********* helpers *********/
.floatRight { float: right; }
.floatLeft  { float: left; }
.right  { text-align: right; }
.left   { text-align: left; }
.center { text-align: center; }
.clear, .clearer { clear: both; }
.block  { display: block; }

// javascript to go into head of document or external .js file

function ahah(url, target) {
  document.getElementById(target).innerHTML = ' Fetching data...';
  if (window.XMLHttpRequest) {
    req = new XMLHttpRequest();
  } else if (window.ActiveXObject) {
    req = new ActiveXObject("Microsoft.XMLHTTP");
  }
  if (req != undefined) {
    req.onreadystatechange = function() {ahahDone(url, target);};
    req.open("GET", url, true);
    req.send("");
  }
}  

function ahahDone(url, target) {
  if (req.readyState == 4) { // only if req is "loaded"
    if (req.status == 200) { // only if "OK"
      document.getElementById(target).innerHTML = req.responseText;
    } else {
      document.getElementById(target).innerHTML=" AHAH Error:\n"+ req.status + "\n" +req.statusText;
    }
  }
}

function load(name, div) {
        ahah(name,div);
        return false;
}

// call code with the name of the external file and the id of the div you want to put the content into

<a href="file1.html" onclick="load('file1.html','content');return false;">File 1a>