All are good. I really enjoyed these authors when I was 7-8. I really balled my head off during some scenes in these books so be prepared. ( When Cafall was killed, I was totally wiped out. )
http://en.wikipedia.org/wiki/The_Dark_Is_Rising_Sequencehttp://en.wikipedia.org/wiki/Madeleine_L'Engle
http://en.wikipedia.org/wiki/The_Chronicles_of_NarniaMore mature themes - 9+
http://en.wikipedia.org/wiki/J._R._R._Tolkienhttp://en.wikipedia.org/wiki/Podkayne_of_Marshttp://en.wikipedia.org/wiki/The_Mote_in_God%27s_Eye
http://en.wikipedia.org/wiki/Paradise_LostYou will want to have access to an OED or Wikipedia or an annotation when doing Paradise Lost.
There are some very good adaptions of JRRT to audio books. The BBC has an EXCELLENT adaptation that makes for great listening.
Brian Fagan has some very good works on history and its interelationship with climate. I attended a lecture of his when I was 12.
http://www.brianfagan.com/The Cosmos series by Carl Sagan is available from Netflicks or you can DVR it. It touches on a number of subjects.