I found Justin Cook's Customizable Digg This! module extremely useful and I liked that it was a module, since installing a plug-in seems a bit of overkill for this sort of thing. Only problem was, Digg This! could only run on Joomla 1.5 when Legacy mode was activated. I've patched the module so it will run native on 1.5 and the free download is here.
Digg This! is a module that will automatically generate a link for each article on your site for submission to Digg.com. You can install it like a standard module (see the Installing Modules article if you don't know how) and you can configure it to appear on any page. I customized a module position on my template so the Digg icon would appear centered about the article.
If you are using Joomla 1.0, go to Justin Cook's site here.
If you want to use a Joomla 1.5 native version, download this:
Download the Digg This! module for Joomla 1.5