I feel obligated to unsubtly pitch #scificlub. Mostly short stories and such, not always good, but oh boy does the material have a pretty broad range. I'm curious what Vonnegut you would recommend. I've hardly read any and I've been meaning to get into him.
Personally I'd recommend Cat's Cradle. Reddit seems to swear by Sirens of Titan and Slaughter House Five is supposed to be his opus but I like the satire of religion in Cat's Cradle. Sirens of Titan seemed too pulpy to me, it's an early work and lacks a lot of his more biting satire of society and human nature. Slaughterhouse Five is a WWII book that could probably stand on its own without the sci-fi. Cat's Cradle the sci-fi is essential and he basically makes fun of religion and human nature in general for 300 pages so I think it's got the right balance of what he does. Here's a short story of his just for fun in case you haven't read it. "Harrison Bergeron"