Ask an Expert Sites Index
Grades: All
Ongoing? Yes
This exceptionally helpful index classifies the many ask-an-expert sites into curriculum-related categories. (Courtesy of the CIESE Project at Stevens Institute of Technology)

Ask the Space Scientist
Grades: K-12
Ongoing? Yes
This site has answered over 24,000 questions from students around the world since August 1995. Visit this site to find answers to questions like: Did ancient peoples really predict solar eclipses? and How are satellites prevented from crashing into each other? Or better yet, ask your own question!

Famous Albertans - Its People and History
Grades: K-8
Ongoing? No
Need a creative way to motivate your students’ interest in their local history? This Canadian page provides an example of student research and artwork about famous Albertans from the past. As part of the project, student visitors to the Web site asked the student researchers questions, which were later posted and answered on the site. The project’s host class also created and shared a timeline of local history and a bibliography from their research work. This project shows how teachers and students can meld history, art, and language arts curricula.

LibrarySpot.com's Ask an Expert Feature
Grades: All (but probably most useful for secondary-level students)
Ongoing? Yes
LibrarySpot's review of ask-an-expert sites, with several high-quality examples featured. Good pointers on how to select the most appropriate ask-an-expert service for learners' questions.

The Mad Sci Network 
Grades: All
Ongoing? Yes
This "collective cranium of scientists" answer just about any type of science question...Here are a few to whet your appetite: Why is my refrigerator door harder to open the second time? How much does the average seahorse weigh? Was the Big Bang actually silent? How is it that blood looks green underwater? The scientist use casual, age-appropriate, and friendly language to answer students' queries.