Downtown on Fremont St is more and more becoming one of my go-to spots when in Vegas for a quick weekend getaway and I'm not feeling like doing anything huge or ridiculous, like pay exorbitant fees to get into a jam-packed nightclub with overpriced drinks and nothing but EDM blasting through the speakers for everyone to jump or flail to (notice how I did not say "dance to").
Commonwealth is right up your alley as far as a chill night in the city is concerned: don't have to be on any guestlist or wait in a huge line or pay a huge cover. The different craft beers are great, the cocktails are excellent, the DJ spins awesome music. Upstairs there's a rooftop "sky bar" where you can chill and enjoy the night, overlooking Fremont St.
Try the banana bread beer and my favorite: the Men in Tights cocktail (for all you whiskey lovers).
-civilities.