Question and answer Search Engines

Human answers

* Answers.com
* eHow
* Uclue
* Yahoo! Answers
* Stack Overflow
* DeeperWeb

Automatic answers

* AskMeNow
* BrainBoost
* True Knowledge
* Wolfram Alpha

Natural language

* Ask.com
* Bing (Semantic ability is powered by Powerset)
* BrainBoost
* hakia
* Lexxe
* Powerset