Here are some links that I've found useful in past. I hope that you may like some of them, too!
Periodic Tables with good info and videos showing properties of the elements:
http://www.chemicool.com/
http://www.periodicvideos.com/
Free Lapbook: http://www.homeschoolshare.com/periodic_table.php
Water Science:
(use with earth science or chemistry)
http://ga.water.usgs.gov/edu/index.html
http://www.nps.gov/archive/wica/Hydrology/PDF.htm
http://earth.usc.edu/~stott/Catalina/Oceans.html
http://www.tulane.edu/~sanelson/geol111/streams.htm
Chemistry:
http://www.alkaseltzer.com/as/student_experiment.html
Chem lapbook and unit study: http://www.homeschoolshare.com/chemistry.php
How Fireworks work: http://www.pyrouniverse.com/consumer/howtheywork.htm
Chem4Kids: http://www.chem4kids.com/
http://www.sciencespot.net/Pages/kdzchem.html
http://reachoutmichigan.org/funexperiments/agesubject/chemistry.html
http://mypages.iit.edu/~smile/cheminde.html
http://education.jlab.org/index.php
Sewage treatment: http://www.chemistrydaily.com/chemistry/Sewage_treatment
Treating the Public Water Supply:
http://www.chemistry.wustl.edu/~edudev/LabTutorials/Water/PublicWaterSupply/PublicWaterSupply.html
Changing plastic to oil: http://www.flixxy.com/convert-plastic-to-oil.htm
How Stuff Works website (good for physics, etc., too):
http://www.howstuffworks.com/
How products are made: http://www.madehow.com/index.html
Physics:
http://www.physics4kids.com/
Thomas Edison lapbook: http://www.homeschoolshare.com/by_resources_thomasedison.php
Math:
Robinsunne's Multiplication Clock:
http://robinsunne.com/robinsunnes_multiplication_clock
MEP math curriculum: http://www.intermep.org/
Order of operations worksheets: http://www.teach-nology.com/worksheets/math/order/
Charts and Graphs: http://www.squidoo.com/chartsandgraphs
Online Space Science curriculum:
http://amazing-space.stsci.edu/capture/
Earth/Sky Tonight: http://earthsky.org/tonight
Cosmos4Kids: http://www.cosmos4kids.com/index.html
http://stardate.org/nightsky/weekly
http://www.botproductions.com/stellar/index.html
http://spaceplace.nasa.gov/en/educators/news/index.shtml
Onlines Earth Science curriculum:
http://www.agiweb.org/earthcomm/geosphere/platetectonics/activity1.html?State=
Dirt, the Movie: http://dirtthemovie.org/
Soil Science: http://soil.gsfc.nasa.gov/basics.htm
Lesson plans: http://www.middleschoolscience.com/earth.htm
Geography 4 Kids: http://www.geography4kids.com/files/earth_intro.html
(really covers geology)
Oregon State's earth science curriculum: http://volcano.oregonstate.edu/plate-tectonics (their website also has lots of videos, photos, games, etc.
Savage Earth, online: http://www.pbs.org/wnet/savageearth/index.html
Plate tectonics: http://scign.jpl.nasa.gov/learn/index.htm
RocksforKids: http://rocksforkids.com/index.html
USGS Volcanoes: http://egsc.usgs.gov/isb/pubs/teachers-packets/volcanoes/
Mineral information: http://www.mii.org/
Minerals and Molecules (can be used with chemistry, too):
http://virtual-museum.soils.wisc.edu/displays.html
Biology resources:
http://www.biologycorner.com/
Plants: http://www.mbgnet.net/bioplants/
Biology for Kids: http://www.biology4kids.com/files/studies_scimethod.html
Drawing with Children, Nature Journal Style: http://www.squidoo.com/drawingwithchildrennature
Nature Study using Comstock's book: http://handbookofnaturestudy.blogspot.com/2008/06/green-hour-name-and-logo-changes-or.html
Hands-on Biology: http://serendip.brynmawr.edu/sci_edu/waldron/
Cells Alive! http://www.cellsalive.com/
Immune Attack game: http://www.fas.org/immuneattack/
Neuroscience for kids: http://faculty.washington.edu/chudler/chmodel.html
Trees: http://www.treesforyou.org/
http://www.butler.edu/herbarium/treeid/treeparts.html
The Visual Dictionary: http://www.infovisual.info/volume_en.html
Parts of a plant cell: http://ghills.metamora.k12.il.us/webquest/5th/plants/plantcell.htm
Parts of a plant: http://www.botanical-online.com/lasplantasangles.htm
Plant structure: http://www.emc.maricopa.edu/faculty/farabee/BIOBK/BioBookPLANTANAT.html
Real Trees 4 Kids: http://www.realtrees4kids.org/
Secrets of Plant Genomes: http://www.plantgenomesecrets.org/
Life science lesson plans: http://www.smithlifescience.com/PH001LessonPlans.htm
The Great Plant Escape game: http://urbanext.illinois.edu/gpe/index.html
Plant labeling: http://www.botanical-online.com/lesplantesactivitat9angles.htm
Biomes and Ecosystems: http://www.mbgnet.net/index.html
Classification (but it's outdated):
http://www.schools.utah.gov/curr/Science/core/7thgrd/sciber7/Classify/html/INTRO.HTM
Ecology: http://www.audubonnaturalist.org/default.asp?page=772
Kids Do Ecology: http://kids.nceas.ucsb.edu/
Mixed Science:
http://www.edheads.org/
http://www.amnh.org/ology/index.php
http://www.msnucleus.org/
http://classroom.jc-schools.net/sci-units/bio.htm#5
http://eequalsmcq.com/
Worksheets: http://www.worksheets4teachers.com/sciencesheets.php
The Story of Stuff (et al): http://www.storyofstuff.com/
Science News for Kids: http://www.sciencenewsforkids.org/pages/search.asp?catid=29
How to Teach Science: http://www.howtoteachscience.com/index.shtml
Forensic Science:
http://bsapp.com/forensics_illustrated/index.html
Medical Mysteries game: http://medmyst.rice.edu/index.html
Literature Study Guides:
http://www.cummingsstudyguides.net/
Literary Elements and Devices (lessons):
http://www.kimskorner4teachertalk.com/readingliterature/literary_elements_devices/menu.htm#Advance
Metaphor worksheets: http://bogglesworldesl.com/metaphor_worksheets.htm
Lesson plans: http://www.cloudnet.com/~edrbsass/edadolescentlit.htm#shortstories
Mythology links: http://www.rcs.k12.va.us/csjh/mytholog.htm
Myths and legends teacher's info links: http://home.comcast.net/~chris.s/mythold.html#persian
Prehistoric Novels bibliography: http://www.trussel.com/prehist/juv.htm
Baldwin Project, old books online:
http://www.mainlesson.com/main/displayarticle.php?article=feature
Children's Books of the Ancient world, bibliography:
http://www.uky.edu/AS/Classics/kidsklassics.html
Online books: http://www.classicreader.com/browse/3/title/
http://www.bartleby.com/
http://publicliterature.org/
http://www.perseus.tufts.edu/hopper/
http://www.fiction.us/
International Children's Digital library (w/ picture books online, in color):
http://en.childrenslibrary.org/
Early Modern poetry online:
http://en.wikisource.org/wiki/Category:Early_modern_poetry
Shakespeare Notebook pages: http://www.homeschoolshare.com/shakespeare_notebook_pages.php
Phrases coined by Shakespeare:
http://www.phrases.org.uk/meanings/phrases-sayings-shakespeare.html
History:
Ancient history: http://ancienthistory.mrdonn.org/index.html
http://www.archaeological.org/pdfs/education/cargoes/Cargoes_Chapter15.pdf
Vikings Study Guide (5 lessons):
http://www.ncte.ie/viking/less1.htm
Viking ship construction: http://www.regia.org/Ships1.htm
Viking study and lapbook: http://www.homeschoolshare.com/viking_adventure.php
Anglo-Saxons: http://www.woodlands-junior.kent.sch.uk/Homework/saxons.htm
History's Happening! Lessons for all historical time periods:
http://www.loeser.us/timemenu.html
more history and lit: http://www.macspage.com/research.html#MedievalEurope
Western tradition videos: http://www.learner.org/resources/series58.html?pop=yes&pid=819#
http://www.historyguide.org/
Make a medieval book: http://www.vam.ac.uk/vastatic/microsites/1220_gothic/make_book.php
Medieval games: http://medievaleurope.mrdonn.org/games.html
Middle Ages: http://medievaleurope.mrdonn.org/index.html
http://www.historyforkids.org/learn/medieval/index.htm
http://www.kathimitchell.com/middleages.htm
http://westernreservepublicmedia.org/middleages/overview.htm
Norman Conquest: http://www.mrfield.btinternet.co.uk/Conquest/index.htm
British Battles (from Norman Conquest onward): http://www.britishbattles.com/braddock.htm
Conquest of Constantinople: http://www.reformation.org/fall-of-constantinople.html
Discovery and Exploration Notebooking: http://www.squidoo.com/discovery-exploration
Timeline Index: http://www.timelineindex.com/content/home/forced
U.S. History using foldables (lapbooking): http://ushistory.pwnet.org/links/foldables.php
U.S. Historical Maps: http://www.lib.utexas.edu/maps/histus.html#early.html
American History AP Quizzes: http://www.historyteacher.net/USQuizMainPage.htm
Voyageurs Study Guide: http://www.mackinacparks.com/Userfiles/File/CM_Adventure_JP.pdf
Boston Tea Party Lapbook: http://www.homeschoolhelperonline.com/lapbooks/boston_tea_party.htm
U.S. History Lesson Plans (also many other subjects): http://www.downloadlearning.com/topics/8/
Texas Indians Activity Guide: http://www.downloadlearning.com/topics/8/
American Revolution Lapbook: http://hebrews110.wordpress.com/free-stuff/
Oregon Trail Lapbook: http://lapbooklessons.com/OregonTrailLapbook.html
http://dynamic2moms.webs.com/westwardhooooo.htm
World History Quiz:
http://www.funtrivia.com/trivia-quiz/ForChildren/World-History-for-Kids-286912.html
British Kings and Queens Printables:
http://www.activityvillage.co.uk/british_kings_and_queens_printables.htm
Maps: http://www.fsmitha.com/maps.html#h1
Geography:
Study of India:
http://www.uni.edu/gai/India/India_Lesson_Plans/India_Lessons.htm
Tons of geography resources: http://home.comcast.net/~tbrown117735MI/Maps.html
A wide variety of Lesson Plans for many, many topics:
http://www.csun.edu/~hcedu013/plans.html#Lesson%20Plans
http://www.enchantedlearning.com/
Constitution Day Lessons for all grade levels:
http://www.k12.com/events/constitution_day_lessons/
Democracy in America lesson plans: http://www.learner.org/resources/series173.html
Art History/Appreciation Resources on the web:
http://witcombe.sbc.edu/ARTHLinks.html
http://gardenofpraise.com/art.htm
Middle school art lesson plans: http://lessonplancentral.com/lessons/Art/Middle_School/index2.htm
Music appreciation:
http://www.classicsforkids.com/
http://www.alaska.net/~tiptoe/webquest/
Orchestra lapbook: http://www.homeschoolhelperonline.com/lapbooks/orchestra.htm
Philosophy for Children:
http://www.mtholyoke.edu/omc/kidsphil/stories.html
Grammar:
KISS grammar curriculum: http://home.pct.edu/~evavra/KISS.htm
Language arts (lit, writing, grammar, etc.): http://guest.portaportal.com/vsprague1
Bible Study for younger children: http://www.geocities.com/~perkinshome/childrennew.html
Free Lapbooks: http://dynamic2moms.webs.com/
http://hebrews110.wordpress.com/free-stuff/