More:

http://www.geocities.com/EnchantedForest/Mountain/9112/Piolife.html

http://www.bchm.org/Austin/panel34.html

http://www.edu.pe.ca/southernkings/pioneer.htm (cute pictures here)

You want links on unit studies on history- here you go:
http://killeenroos.com/links.htm

These ones are science:
http://teachers.hypermart.net/links/pages/Free_Unit_Studies/Science/
http://www.ericse.org/slessons.html

More:
http://www.learninghaven.com/Unit%20Studies.htm