The Culture, the galaxy
-spanning pan-species civilization
around whom the science fiction books of Iain M. Banks
are set, is a utopia in the purest sense of the word.
It is a society in which all sentience is respected, whether it be humanoid, alien or machine. The Culture has no rulers or actual system of government. The only holders of power are the Minds, incredibly intelligent sentient machine intelligences. The Minds are the minds of entire ships, space stations, planets. The Mind will take care of all of the sentient beings living on it, if it chooses to have any beings live on it.
The fact that a Mind, even one of a space station purpose-built to house humans, can choose not to have any beings living on it, is a part of the beauty of the Culture. The Culture stands for absolute freedom. Anything is permitted; the citizens of the Culture barely know the meaning of the word "forbidden". The only act which is truly not permitted in the Culture is murder, although if a person commits it there is no penalty. They are merely observed closely enough so that it is impossible for them to kill again.
The futuristic technology of the Culture is amazing. Classical advances, such as greater-than-light speeds and super-intelligent AIs, are alongside more original concepts such as the amazing genetic alterations (geno-fixing) which all Culture citizens undergo. A huge variety of recreational and useful drugs can be produced inside the average Culture citizen's body, and one is even able to change gender autonomously, via a virus which changes the person's sex in a gradual process, taking around 15 months to completely change gender.
The Culture takes the general view that, although it realizes that its collective view of morality is completely subjective, it should try to do the best that it can to help less developed societies in a covert way, and to ameliorate the effects of dictatorships and the like. The sections of the Culture which deal with these sensitive matters are known as Contact and Special Circumstances.
The human inhabitants of the Culture have no need to concern themselves with anything but enjoying themselves, and living their life to the utmost fulfillment. This may sound reminiscent of such "utopias" as the Brave New World, but the Culture's is an infinitely more pleasant concept. Citizens, being geno-fixed, have a natural lifespan of about 300 years. If they so wish, their age can be stabilized so that they are immortal, barring violent death(rare) or euthanasia.
The Culture, to me, seems an idyllic place, without any real societal flaws. However, this is just what it is: an ideal, not a reality, one which it seems impossible to reach.