I've got a Heinlein, a Clarke and an Asimov in my list. Dune? Dune is the least shit book of a shit series. Stephenson? Yeah, Snow Crash is Neuromancer with puns. Stick to William Gibson. Sorry about your cat, but "essential" sci fi doesn't have to include stuff that only nerds like.
I think non-nerds would enjoy Dune more than Ringworld, for instance. Yeah, it's a shit series, and by far not the best written sci-fi book ever, but it is a purely enjoyable and epic story. I think a large part of it's value is that the sci-fi components tend to act more as an accompaniment to the plot rather than as major devices themselves.
I finished Dune a while back, but I just started reading Dune Messiah. I'm about 2 or 3 chapters in... should I stop now?