Right, Banks' Culture seems fairly mainstream and because it doesn't need to make episodic adventures it often gets to actually do utopian stuff Trek wouldn't even if only as a backdrop to the exciting story. The repeated instances in which Culture children play happily, insulated from whatever terrifying stuff we're reading about is an example.

Or if Comic Books are in scope, obviously "Miracleman: The Golden Age" is a utopia. Explicitly so. It is about the ways people are still people in a utopia.

Less mainstream, Greg Egan's Amalgam is also clearly a utopia. The couple in "Riding the Crocodile" choose to die at the end of that story, more out of some sense that stories need endings than because of any outside force.