Bibliography creator

NoodleTools-QuickCite
http://www.noodletools.com/quickcite/citbook.html

Explorers and exploration

Social Studies for Kids
http://www.socialstudiesforkids.com/subjects/explorers.htm

Cyber Sleuth Kids
http://cybersleuth-kids.com/sleuth/History/Explorers/

Kid Info.
http://www.kidinfo.com/American_History/Explorers.html

Kids Connect
http://www.kidskonnect.com/subject-index/16-history/265-explorers.html

Math - Subtracting negatives

Math is fun
http://www.mathsisfun.com/positive-negative-integers.html

Centre for innovation in Mathematics teaching
http://www.cimt.plymouth.ac.uk/projects/mepres/book7/bk7i15/bk7_15i1.htm

Native Americans

Native American Facts for Kids: resources on American Indians for children and teachers
http://www.native-languages.org/kids.htm

Periodic Table

An online, interactive periodic table of the elements
http://chemicalelements.com/

WebElements: the periodic table on the web
http://webelements.com/

Chemi Cool
http://chemicool.com/

A periodic table of the elements resource for Elementary, Middle, and High School students
http://periodic.lanl.gov/default.htm

Jefferson Lab: It's elemental
http://education.jlab.org/itselemental/

States and Capitals

Sheppard software: U.S.A. games
http://www.sheppardsoftware.com/web_games.htm