joetan

A simple pre-filter to weed out the most obvious comment spam (about 90% of all spam).
Legitimate comments that get blocked (either by this plugin or by Akismet) can be presented with a captcha to confirm that the comment is legitimate. Comments that don’t pass the captcha will be immediately discarded.
Helps you identify potential spam words (you can use this to tweak the plugin’s filters).

TanTanNoodles Simple Spam Filter

A plugin that does a simple sanity check to stop really obvious comment spam before it is processed.

Comment spam is annoying, and although there are great plugins like Akismet 
to catch spam, annoying “this is best post evar” compliment spam seems to 
always wiggle through. The best way to tell if a compliment is genuine 
is to check Google to see if it’s been slathered all over the web.
Auto-querying Google is against the ToS, so this plugin just gives you 
convenient link to do the check.

O RLY

O RLY Comment Spam Search creates a quick link to make sure comments aren't spam.

TanTanNoodles Simple Spam Filter vs O RLY