There was some other Card book I read, a gift to me from a brother, but can't remember much about it now, only that I couldn't get into the sequel.
As for the hours wasted watching the four movies you listed, I think maybe I wasted about an hour total. That is, I liked Dune. I thought I, Robot was okay, not great and not bad. I liked Hitchhiker's Guide the the Galaxy, and didn't bother with The Postman because it just didn't look interesting at all.
Of those four, I've read the radio-script for Hitchhiker's Guide and listened to it, and watched the TV series, and listened to the vinyl album, and read the five books of the trilogy, and watched the movie. In my opinion, they're all hilarious, and have Adams' hand in all of them.
I didn't know there was a book for The Postman, and if the movie's plot is the same as the book, then I'm still not interested.
Never was an Asimov fan. Make a movie of A.E. van Vogt's Slan sometime instead.
Hated Dune (the book.) I tried to read it, several times, even an illustrated copy. Still couldn't get more than twenty pages into it. I've had friends tell me, and I quote "If you just get past the first 100-200 pages, it's a great book!" Yeah, well, 100-200 pages is regular-sized novel to me. If you can't get to the good stuff within the first twenty pages, then don't expect me to keep reading.
So, I'll probably see Ender's Game, at least on Dish, and I doubt I'll waste nearly as much of my time as I did honestly attempting to read one of the "great" novels of science fiction.