Add-ons: Spammenot

Are you tired of gold farmer spam? Sick of seeing immature boys linking spells and items along with body part references? Then you need Spammenot!

From the developer's comments:

SpamMeNot intelligently detects, blocks and reports commercial and annoying spam messages before you even see them

Also:

SpamMeNot is being [has been] completely rewritten for the Wrath of the Lich King Expansion.

• Configurable spam score level means you can tighten up the spam detection or relax it as you desire.
• The level it auto-reports at is also configurable.
• Monitors the trade channel for people linking an exceptional amount of spell links as well as keywords such as "An*l" and "Dirge" and will flag and auto-report participants of mass trade spam.
• 3rd party AddOns can ask SpamMeNot to filter their events via it's API.
• Nicer configuration interface.
• Much more organized internal structure.
• Less chance of causing code taints.

You can get Spammenot from Curse or through Wowmatrix.