If you're in the mood for something quick, I recommend keeping around either of these:Shine: An Anthology of Optimistic Science-FictionA Good Old-Fashioned Future
Both of these contain stories that are, well, as Shine
says: optimistic. They aren't utopian, just contain the belief that humanity is good at the core, and therefore, in the long run, so will our world be. We will have struggles to overcome, and we WILL.
I'd also recommend Ray Bradbury's works. His short story collections are all excellent. The Martian Chronicles and From the Dust Returned are both short story collections that re-use the same characters, creating a cohesive overall narrative (is there a technical name for this type of 'framed anthology'?). The former, of course, is of a future where we colonize Mars; the latter is a more serious take on an Addams Family-like clan of supernaturals (he and Charles Addams actually considered collaborating on the Addams Family before going their separate ways with the core concept, and C.A. did several illustrations for Bradbury's books). My personal favorite book, though, is one of his full-length novels: Something Wicked This Way Comes. There's just so much depth there, and it's a great source material for RPG inspiration, too.