There's actually a pretty cool storyline in the (now defunct) EMPIRE comic series that deals with some of this. I think it was called "Shadows of their fathers".
Basically it's set between ANH and ESB, but relates to the Clone Wars storyline "Last stand on Jaabim", where Anakin is forced (Mainly on Palpatine's orders) to withdraw and leave a group of Republic fighters to the seperatist army. Years later, Luke goes to the planet, and begins to learn that his father wasn't exactly the great hero he thought he was. Plus Vader's in the story too, of course. Luke at the end of the story, realizes that Obi-Wan wasn't exactly telling him 100% of the truth, and wonders what else he doesn't know about his father...
There are also the novels by Troy Denning, which although they take place after ROTJ, they have Luke and Leia gradually learn about what happened in the prequels and who their mother was.
The Clone Wars comic arc "Last Stand of Jabiim" was my favorite. Good, dark story with what becomes a very bloody battle. I thought afterwards it would be great if Luke ever visited the planet and low and behold, Empire does a big story arc on it.
In the SW Annotated Screenplays books (published 97-98), Lucas said he wanted one of the twins to have a memory of their mother. Though he very clearly reversed himself in the prequels.
I've never known why Lucas has felt the need to lie and say that the nine movie thing was just a media creation. There's a ton of stuff from LFL saying there would be nine movies (very early on even 12) and Lucas himself hints at it in the foreword to the 20th anniversary of the Splinter in the Mind's Eye book. In the recently published The Making of The Empire Strikes Back book, there's an old interview where he says he went a little overboard with how many movies there were. He says that seven were planned originally. I think that he originally thought nine but realized he could wrap it up a lot sooner and also realized it would take years to do another trilogy. The prequels took him about 11 years from start to finish. If he changed his mind, that's certainly his choice and I can understand why. But there's no reason for him to lie and claim that nine movies was a media creation.
That same Empire book contains an old interview with Mark Hamill where he wonders if Alec Guiness knew that Vader was Luke's father. He points out a scene I think everyone picks up on. When Luke asks how his father died, Obi-Wan looks away for a moment before starting. It's the look of a man who doesn't want to tell him the truth and is hiding something. It totally works for me. As another poster observed, Darth Vader in Dutch means "Dark Father." So I'm inclined to believe GL more when he says the connection was planned out from the beginning. Luke and Leia were twins I believe in the second draft of ANH but it's clear that's not what GL was thinking in ANH and ESB. There is a scene or two cut out of ESB where Luke and Leia are on on the verge of a passionate kiss.