Displaying the last modified date can be really useful for articles and informative blogposts - especially for people doing their research essay at the last minute *cough*
All you really need is this simple javascript:

<script type="text/javascript">document.write (document.lastModified);</script>

This will display as:
This page was last modified on:…

If you want to add in a simple button or link for visitors to refresh the page, there is a really simple code that does the trick

Button

<FORM>
<INPUT TYPE="button" VALUE="Reloadthe page" onClick="history.go(0)">
</FORM>

Link

<a href="#" onClick="history.go(0)">Refresh the page!</a>

Refresh the page!