<script type="text/javascript">

_spBodyOnLoadFunctionNames.push("cleanLinks");

function cleanLinks(){

  var baseURL = "http://google.com/";

  var len = baseURL.length;

  var links = document.getElementsByTagName("a");

  for (var i=0; i < links.length; i++) {

    if (links[i].href && links[i].href.substring(0,len) == baseURL){

      if (links[i].innerText==undefined) {

      links[i].textContent = links[i].textContent.substring(len);

      }

      else{

      links[i].innerText = links[i].innerText.substring(len); //for IE

      }

    }

  }

}

//-->

</script>

Just replace the value of the variable 'baseURL' with whatever you use for a base in your calculated column.  If you also want to clean up the text (like in the case of url-encoded file names or underscores that replace spaces), you'll need the replace() method in both lines that replace the display text (one for Firefox and one for IE).

Technique 2

In this case, we can not predict the "base URL."  So we will clean up our links by replacing the url with the word "link" for any tag using the href attribute as its display text.

<script type="text/javascript">

_spBodyOnLoadFunctionNames.push("cleanLinks");

function cleanLinks(){

  var links = document.getElementsByTagName("a");

  for (var i=0; i < links.length; i++) {

    if (links[i].href && links[i].href == links[i].innerText){

      links[i].innerText = "link";

      }else{

      if (links[i].href && links[i].href == links[i].textContent){

      links[i].textContent = "link";

      }

    }

  }

}

//-->

</script>

A slightly fancier version of that technique adds an image using some embedded CSS:

<STYLE TYPE="text/css" MEDIA=screen>

<!--

.mylink

{

    background-image: url(/_layouts/images/link.gif);

    background-repeat: no-repeat;

    font-family: tahoma,sans-serif;

    font-size: 8pt;

    padding-left: 25px;

}

-->

</STYLE>

<script type="text/javascript">

_spBodyOnLoadFunctionNames.push("cleanLinks");

function cleanLinks(){

  var links = document.getElementsByTagName("a");

  for (var i=0; i < links.length; i++) {

    if (links[i].href && links[i].href == links[i].innerText){

      links[i].parentNode.className="mylink";

      links[i].innerText = "link";

      }else{

      if (links[i].href && links[i].href == links[i].textContent){

      links[i].parentNode.className="mylink";

      links[i].textContent = "link";

      }

    }

  }

}

//-->

</script>