I saw the Khan Academy app a few days ago, and am quite impressed with it. If you want to check your math homework while watching the videos you can use WinFone Alpha, a free Wolfram|Alpha client for windows phone.
You should check out mySocialPhotos ... With the new facebook integration its a must have App. http://social.zune.net/redirect?type=phoneApp&id=7769d0c4-6932-e011-854c-00237de2db9e
@Panda bear:You're not really supposed to nominate your own apps dude - otherwise I would be pointing you towards 'Ambient Soundscape' :