KidsClick! http://sunsite.berkeley.edu/KidsClick!/ Excellent site created by librarians with a search engine of appropriate educational sites for students. Education Planet - The Education Web Guide http://www.educationplanet.com/ This is a searchable collection of educational web sites. Uncheck the boxes except for web sites and maybe maps.
Education World http://db.education-world.com/ Large web site of educational links and a search engine feature to search these links. Schoolwork.org http://www.schoolwork.org/ This is a searchable site of educational web sites.
Awesome Library - Education Search Engine http://www.neat-schoolhouse.org/searche.html Database of 110,000+ sites related to educational topics.
Awesome Library - K-12 Education Directory for Kids http://www.awesomelibrary.org/student.html Search engine with a kids category. (limited results)
Blue Web'n Refined Search http://www.kn.pacbell.com/wired/bluewebn/search.html Search engine of good educational sites, with ratings and grade levels. However, this is a fairly small database, so use one or two keywords only.
LookSmart: Exploring World - Reference & Education k-12 - For Teachers - curriculum content http://www.looksmart.com/r?lm,p&e76280 This is a search engine that searches educational curriculum content information gathered by educational sites.
LookSmart: Exploring World - Reference & Education k-12 - For Teachers - Lesson Plans http://www.looksmart.com/r?lm,p&e62602 This is a search engine that searches lesson plans gathered by a number of educational sites.
The WWW Virtual Library http://www.vlib.org/ searchable collection - may not be just geared to kids