These are the sites I use with my 4th graders.
Website: http://www.classdojo.com/
Free iPad app: http://itunes.apple.com/us/app/classdojo/id552602056?ls=1&mt=8&uo=4&at=10l6SU
Free iPhone app: http://itunes.apple.com/us/app/classdojo/id552602056?ls=1&mt=8&uo=4&at=10l6SU
Free Android Phone app: https://play.google.com/store/apps/details?id=com.classdojo.android
Google Chrome app: https://chrome.google.com/webstore/detail/pbinoojbbajacmkigmfnkclhgjnglpon
Free Android Phone app: https://play.google.com/store/apps/details?id=com.brainpop.brainpopfeaturedmovieandroid
Google Apps for Education app: https://www.google.com/enterprise/marketplace/viewListing?productListingId=8006+9291735389906767602
Free iPad app: http://itunes.apple.com/us/app/brainpop-featured-movie/id364894352?mt=8&uo=4&at=10l6SU
Free iPhone app: http://itunes.apple.com/us/app/brainpop-featured-movie/id364894352?mt=8&uo=4&at=10l6SU
Website: http://www.brainpop.com/
Google Chrome app: https://chrome.google.com/webstore/detail/brainpop-featured-movie/cdikkckjinnmjpgkjjpnfmmbcpbhmklf
Free Android Phone app: https://play.google.com/store/apps/details?id=com.fusionprojects.edmodo
Free iPad app: http://itunes.apple.com/us/app/edmodo/id378352300?mt=8&uo=4&at=10l6SU
Free iPhone app: http://itunes.apple.com/us/app/edmodo/id378352300?mt=8&uo=4&at=10l6SU
Website: http://www.edmodo.com/
Google Chrome app: https://chrome.google.com/webstore/detail/edmodo/fpcdidgjjebefhmlhjlgnkahlimgaemc
Google Chrome app: https://chrome.google.com/webstore/detail/gajclnhcflhoicggnpmgkedchldikjgn
Free iPad app: http://itunes.apple.com/us/app/voicethread/id465159110?mt=8&uo=4&at=10l6SU
Free iPhone app: http://itunes.apple.com/us/app/voicethread/id465159110?mt=8&uo=4&at=10l6SU
Website: http://voicethread.com/
Free Android Phone app: https://play.google.com/store/apps/details?id=com.google.android.apps.docs
Google Chrome app: https://chrome.google.com/webstore/detail/google-drive/apdfllckaahabafndbhieahigkjlhalf
Free iPad app: https://itunes.apple.com/us/app/google-drive/id507874739?mt=8&uo=4&at=10l6SU
Free iPhone app: https://itunes.apple.com/us/app/google-drive/id507874739?mt=8&uo=4&at=10l6SU
Website: http://docs.google.com/
Website: http://edu.glogster.com/product-information/?promo_code=65D3GB
Free iPad app: http://itunes.apple.com/us/app/glogster/id552911140?mt=8&uo=4&at=10l6SU
Free iPhone app: http://itunes.apple.com/us/app/glogster/id552911140?mt=8&uo=4&at=10l6SU
Google Chrome app: https://chrome.google.com/webstore/detail/pgoigcdmeplpebbdfjcofinjnlghmefh
Free Mac program: http://www.techsmith.com/download/jing/default.asp
Free Windows program: http://www.techsmith.com/download/jing/default.asp
Website: http://freerice.com/
Website: https://twitter.com/
Free iPad app: https://itunes.apple.com/us/app/id333903271?mt=8&at=10l6SU
Free iPhone app: https://itunes.apple.com/us/app/id333903271?mt=8&at=10l6SU
Free Android Phone app: https://play.google.com/store/apps/details?id=com.twitter.android
Free Android Tablet app: https://play.google.com/store/apps/details?id=com.twitter.android
Free Mac program: https://itunes.apple.com/us/app/twitter/id409789998?mt=12&uo=4&at=10l6SU
Google Chrome app: https://chrome.google.com/webstore/detail/diigo-bookmark-archive-hi/oojbgadfejifecebmdnhhkbhdjaphole
Mozilla Firefox extension: https://addons.mozilla.org/en-US/firefox/addon/diigo-web-highlighter-and-stic/
Free iPad app: https://itunes.apple.com/us/app/diigo/id417202559?mt=8&uo=4&at=10l6SU
Free iPhone app: https://itunes.apple.com/us/app/diigo-offline-reader/id335006600?mt=8&uo=4&at=10l6SU
Website: http://www.diigo.com/
Website: https://quizlet.com/
Edmodo app: http://www.edmodo.com/publisher?uid=507204
Free iPhone app: https://itunes.apple.com/us/app/quizlet/id546473125?mt=8&uo=4&at=10l6SU
Google Chrome app: https://chrome.google.com/webstore/detail/quizlet/bgofflgeghkhocbociocnckocbjmomjh
Website: http://sites.google.com/
Free iPad app: https://itunes.apple.com/us/app/google-earth/id293622097?mt=8&uo=4&at=10l6SU
Free iPhone app: https://itunes.apple.com/us/app/google-earth/id293622097?mt=8&uo=4&at=10l6SU
Free Android Phone app: https://play.google.com/store/apps/details?id=com.google.earth
Free Mac program: http://www.google.com/earth/download/
Free Windows program: http://www.google.com/earth/download/
Google Chrome app: http://www.google.com/earth/explore/products/plugin.html
Mozilla Firefox extension: http://www.google.com/earth/explore/products/plugin.html
Apple Safari extension: http://www.google.com/earth/explore/products/plugin.html
Website: http://www.symbaloo.com/
Free Android Phone app: https://play.google.com/store/apps/details?id=com.symbaloo.android
Free iPhone app: https://itunes.apple.com/us/app/symbaloo-bookmark-share-your/id521081559?mt=8&uo=4&at=10l6SU
Google Chrome app: https://chrome.google.com/webstore/detail/symbaloo/dfnbdccaiknlpdgabdgjijniolkgmoeh
Website: http://kidblog.org/
Website: http://www.khanacademy.org/
Free iPad app: https://itunes.apple.com/us/app/id469863705?mt=8&at=10l6SU
Free iPhone app: https://itunes.apple.com/us/app/id469863705?mt=8&at=10l6SU
Free Android Phone app: https://play.google.com/store/apps/details?id=org.khanacademy.android
Free Android Tablet app: https://play.google.com/store/apps/details?id=org.khanacademy.android
Edmodo app: https://spotlight.edmodo.com/product/khan-academy,324527/
Website: http://www.easybib.com/
Free iPhone app: http://itunes.apple.com/us/app/easybib/id436768184?mt=8&uo=4&at=10l6SU
Free Android Phone app: https://play.google.com/store/apps/details?id=com.easybib.easybibandroid
Google Apps for Education app: https://www.google.com/enterprise/marketplace/viewListing?productListingId=6357+7423325443125160988
Google Chrome app: https://chrome.google.com/webstore/detail/cbpiiblghhnlalifiaddecedaeaijdpe
Free Mac program: http://scratch.mit.edu/download
Free Windows program: http://scratch.mit.edu/download
Google Apps for Education app: https://www.google.com/enterprise/marketplace/viewListing?productListingId=14101+14209459616553746611
Website: http://www.wikispaces.com/
Website: http://tenmarks.com/
Website: http://www.ixl.com/
Website: http://digitwhiz.com/
Free iPad app: http://itunes.apple.com/us/app/digitwhiz-math/id559968556?mt=8&uo=4&at=10l6SU
Website: http://wowzers.com/
Website: http://www.discoveryeducation.com/
Website: http://wonderopolis.org/
Website: http://www.tynker.com/
Free iPad app: https://itunes.apple.com/us/app/tynker-learn-programming-visual/id805869467?mt=8&uo=4&at=10l6SU
Website: https://www.funbrain.com/
Website: http://www.thinkfinity.org/
Website: http://interactivesites.weebly.com/
Website: http://www.mathplayground.com/
Website: https://storybird.com/
Website: http://www.tagxedo.com/
Website: http://www.thinglink.com/
Free iPad app: https://itunes.apple.com/us/app/thinglink/id647304300?mt=8&uo=4&at=10l6SU
Free iPhone app: https://itunes.apple.com/us/app/thinglink/id647304300?mt=8&uo=4&at=10l6SU
Website: http://www.spellingcity.com/
Edmodo app: http://www.edmodo.com/publisher/vocabularyspellingcity
Free iPhone app: https://itunes.apple.com/us/app/spellingcity/id538407602?mt=8&uo=4&at=10l6SU
Free iPad app: https://itunes.apple.com/us/app/spellingcity/id538407602?mt=8&uo=4&at=10l6SU
Website: http://todaysmeet.com/
Free Android Phone app: https://play.google.com/store/apps/details?id=com.skype.raider&hl=en
Free iPad app: http://itunes.apple.com/us/app/skype-for-ipad/id442012681?mt=8&uo=4&at=10l6SU
Free iPhone app: http://itunes.apple.com/us/app/skype/id304878510?mt=8&uo=4&at=10l6SU
Free Mac program: http://www.skype.com/go/download
Free Windows program: http://www.skype.com/go/download
Website: http://skype.com/
Free Mac program: http://www.openoffice.org/
Free Windows program: http://www.openoffice.org/
Website: http://www.voki.com/
Website: http://bighugelabs.com/
Free Android Phone app: https://play.google.com/store/apps/details?id=com.studyblue
Free iPad app: http://itunes.apple.com/ie/app/studyblue/id323887414?mt=8&uo=4&at=10l6SU
Free iPhone app: http://itunes.apple.com/ie/app/studyblue/id323887414?mt=8&uo=4&at=10l6SU
Website: http://www.studyblue.com/
Google Chrome app: https://chrome.google.com/webstore/detail/studyblue-inc/hiicppnmnhhkaaboclnefgkbnpkompmh
Website: http://kids.nationalgeographic.com/
Website: http://www.readwritethink.org/
Website: http://www.instagrok.com/
Free iPad app: https://itunes.apple.com/us/app/instagrok/id777873941?mt=8&uo=4&at=10l6SU
Google Apps for Education app: https://www.google.com/enterprise/marketplace/viewListing?productListingId=17789+13349884249762973052
Google Chrome app: https://chrome.google.com/webstore/detail/instagrok/flonaffkffjppejcafgpdgilebfikemd
Edmodo app: http://www.edmodo.com/publisher?uid=7493337
Website: http://bensguide.gpo.gov/
Website: http://www.enchantedlearning.com/
Paid Mac program: http://www.bigbrainz.com/Cool-Math-Games.php
Paid Windows program: http://www.bigbrainz.com/Cool-Math-Games.php
Website: http://www.sumdog.com/
Website: http://www.tutpup.com/
Website: http://www.gamequarium.com/
Website: https://www.bbc.co.uk/bitesize
Website: http://learnzillion.com/
Website: http://www.scootpad.com/
Edmodo app: http://www.edmodo.com/publisher/scootpad
Google Chrome app: https://chrome.google.com/webstore/detail/scootpad/boihgpoojeingjbbdjmoocbdibophjap
Free Mac program: https://itunes.apple.com/us/app/scootpad/id493083432?ls=1&mt=12&uo=4&at=10l6SU
Free Android Phone app: https://play.google.com/store/apps/details?id=com.scootpad.app
Free iPad app: https://itunes.apple.com/us/app/scootpad/id557056479?mt=8&uo=4&at=10l6SU
Free iPad app: https://itunes.apple.com/us/app/time-for-kids-family-edition/id550252887?mt=8&uo=4&at=10l6SU
Free iPhone app: https://itunes.apple.com/us/app/common-sense-media-kids-media/id504932051?mt=8&at=10l6SU
Website: http://www.commonsensemedia.org/
Free iPad app: https://itunes.apple.com/us/app/common-sense-media-kids-media/id504932051?mt=8&at=10l6SU
Free Android Phone app: https://play.google.com/store/apps/details?id=com.csm.KidsMedia
Free Android Tablet app: https://play.google.com/store/apps/details?id=com.csm.KidsMedia
Website: http://www.abcya.com/
Website: http://teacher.scholastic.com/products/bookflixfreetrial/
Website: http://www.storylineonline.net/