Different methods to make a null link?

You just want something you can shove in the <a> tag? OK:

<a href="#" onclick="return false;">Example</a>

Combine it with any of the href= methods from your question.

Given that a link that doesn't go anywhere is fairly useless, can I assume you want to kick off some JavaScript function when the link is clicked? If so, do this:

<a href="#" onclick="yourFunctionHere(); return false;">Example</a>

The # method is the simplest, and is always compatible. Using a href=# however, will jump to the top of the page. To prevent the jump, simply reference an unnamed anchor. Like this:

<a href=#nothing >This link has a null href!</a>

<a href=#doesnotexist >This link has a null href!</a>

<a href=#null >This link has a null href!</a>

<a href=#void >This link has a null href!</a>

<a href=#whatever >This link has a null href!</a>