Marco Luthe Online!

This plugin has two functions: you can (a) shorten links in your comments so that they do not mess with your template design and (b) you can get rid of the “rel=nofollow” attribute which WordPress includes in each of those comment links.

• “GoodLinks” for WordPress:
  www.alphamarkus.de/?page_id=12

PS:
There are other plugins that can delete the “rel=nofollow”attribute, but I thought this one is quite nice because it also has that other feature. If you are looking for more comment plugins, you might also have a look at Lorelle VanFossen’s post WordPress Plugins For Comments.

[Update from 2007-06-17]

I decided to go with a single solution for truncating URLs in comments (using wp-chunk) and getting rid of the “nofollow” attribute (using Dofollow), because I had some issues with GoodLinks: URLs were not being shown in comments.