These are a few of my favorite Earth and Space Science apps.
Learn Science--use this to cover any topic in science. It has videos about biology, Earth Science, Pollution, etc.
Barron's Painless Earth Science Challenge--use this to quiz yourself after learning a unit or at the end of the semester. Games are unlocked when you pass the quizzes with 80% accuracy.
NASA Science--use this to learn about four major topics (Space Weather, Ice Sheets, Habitable Planets, Life on Mars) and multiple subtopics.
Star Chart--use this to find planets, constellations, and stars.
LongiLati--use this to practice longitude and latitude
Earth Lapse--use this to see views of the earth from different perspectives in space (International Space Station and various satellites).