Akismet is an excellent spam fighting tool, there's no doubt about it. But there are comments that don't look like spam even to the human eye, Akismet has a hard time catching them.
I present you Antispam Extra to help you combat and manage comment spam a little better :) Antispam Extra can do the following:
1. Prevent commenters from submitting their websites.
2. Disable the links to commenters' websites.
3. Deactivate the links in comments.
4. Mark comments without proper HTTP referer as spam.
Hope this plugin comes in handy for those WordPress users who are troubled by user submitted links, in the form of commenter website or links in the comment.
Feedback most welcome.