|Later in his career, Asimov started writing novels that connected the Robot, Empire and Foundation series together into one coherent universe. Although I'm not familiar with them, the fact that there are no robots mentioned in the Foundation series means there's probably some creative hoop-jumping.
There is actually a simple explanation for it. In the Robot series, there were the Earth people and the Spacers, the people who had, hundreds of years before, colonized about 30 or so of the closer viable planets. The Spacers had come to be reliant on robots in their daily lives, and had grown decadent. At one time, Earth and the Spacers fought a war, which ended in a stalemate and resulted in long-standing animosity. The Earth people came to associate robots with the Spacers. Spacers=bad, robots=Spacer, robots=bad. So the people on Earth did not use robots. Now, due to their decadent culture, the Spacers had stopped exploring space and colonizing, AND their population dropped off due to dwindling reproduction rates. The Earth people eventually colonized other worlds, while the Spacers, along with the robots, declined and eventually fell into ruin. Over time, the other people forgot about the Spacers and robots, and thousands of years later, established the Galactic Empire. Over time, the Galactic Empire declined, and the Foundations were created to shorten the interim period between the predicted thousands of years of choas and the rise of the next Empire.
A couple suggestions:
The Dispossessed by Ursula K. Leguin. More of a political treatise than a novel, but really, a fascinating examination of how an actual socialist society would work.
The Mars trilogy by Kim Stanley Robinson (Red Mars, Green Mars, Blue Mars)
The hardest of hard sci-fi. Probably the most detailed and well-researched bit of speculative fiction on Mars colonization. Recommended only for people who can handle pages and pages of meticulously detailed landform descriptions. Hey, and for the troglydytes, it has a Space Elevator, an Antarctic ice shelf melting and flooding Earth, two revolutions, a constitutional convention, and, of course, sex scenes.
The Uplift Series by David Brin (Sundiver, Startide Rising, The Uplift War, Brightness Reef, Infinity's Shore, Heaven's Reach) Space opera doesn't get any better than this.