Comment Learn your roots... (Score 1) 1419
I have to second several mentions here. Giving your kids an opportunity for a good grounding in classic sci-fi/fantasy literature will pay back in spades. I've also added in some more recent enjoyments.
* A.E. van Vogt - just about anything will do
* Andre Norton - again, just about anything
* Edmond Hamilton - _The Best of Edmond Hamilton_ collection
* Leigh Brackett - _The Best of Leigh Brackett_ collection
* Heinlein juveniles - _Time for the Stars_, _The Starbeast_, etc.
* E.E. "Doc" Smith - Lensman hexology
* Asimov - Robots series
* Bester - _Stars my Destination_ is a little mean, but workable
* Clifford Simak - _Time and Again_
* Weis and Hickman - DragonLance Chronicles and Legends trilogies
* Robert Jordan - Wheel of Time series, long and a bit more grown up, but your kids will handle them
* L'Engle - Time Quartet
* Patricia McKillip - Riddle-Master trilogy
* Tolkien - they'll handle the classic four
* Robin McKinley - _The Blue Sword_, _The Hero and the Crown_
* Anne McCaffrey (and others) - Dinosaur Planet series, especially the latter three: _Sassinak_, _The Death of Sleep_, _Generation Warriors_
* C.J. Cherryh - _Downbelow Station_, _Rimrunners_
* Arthur H. Landis - _A World Called Camelot_
* Neal Stephenson - if they like history, _Cryptonomicon_
That's about all my poor brain can dump at this time.