For Older Students -- Search Engines and Directories

BJ Pinchbeck's Homework Helper
Bubl Link
Digital Librarian
Electronic Prodigy
High School Hub
Homework Spot

IMSA 21st Century Information Fluency
Infoplease.com
Internet Public Library

Google Scholar 
Kartoo
Librarian's Index to the Internet

ERIC Website and Search Interface
New York Times Navigator
NoodleQuest

Multiple Search Engines on one Page

Choose the best search engine for your needs  Noodletools
How to Choose a Search Engine
Search Engines for Kids  This includes 3 areas for teachers.