http://sharethis.com/
Or if you need to add extra markup or anything, you can manually embed the links to the post template:
Code:
<a href="http://digg.com/submit?phase=2&url=<?php the_permalink() ?>&title=<?php the_title(); ?>&bodytext=<?php the_excerpt(); ?>">Submit to Digg</a>
<a href="http://twitter.com/home?status=Reading:+<?php the_title(); ?>+<?php echo get_option('home'); ?>/?p=<?php the_ID(); ?>">Tweet this</a>
etc. I have the required code for the main social networking sites, PM me if you want them.