Sci-Fi/Fantasy Favorites

One of my dear friends whom I've known forever & ever... (since '93, I think) is now a missionary teacher in Papua/New Guinea. She's teaching in a Wycliffe school and requesting titles of favorite sci-fi/fantasy titles for 7th-12th graders. Seems their little library has an incredible dearth/paucity/lack of such materials. I've offered many suggestions to her and so has my sister. I thought I'd pass along any new suggestions anyone has to share. Here's the parameters of her search:

1st) What sci-fi/fantasy made a big impact on you when you were young? What would you recommend to almost anyone as an "excellent book"?

2nd) most of her students are young Christians & unprepared to deal with a high level of sensuality/sexuality or extreme violence simply for the sake of violence (her comparison was that "Ender's Game" uses a lot of violence, but it moves the story along and has a reason)...

I've suggested such titles as:
Andre Norton- Star Man's Son
Anne McCaffrey- DragonDrums trilogy
Piers Anthony- A Spell for Chameleon
C.S. Lewis- The Lion, The Witch & The Wardrobe
Robin Mckinley- The Blue Sword

I had more, but can't remember any more off the top of my head. Anyway, what other titles do you all suggest? I'll pass them along to her...