Seeking Sci-Fi Humor without Fantasy – Space Ships, Now Swords and Sandals

I've been reading more and more humor novels. Just finished Being There, The Man with Two Left Feet (my first Wodehouse) and currently reading Three Men in a Boat…but looking for something more speculative, specifically sci-fi humor in the vein of Hitchhikers Guide to the Galaxy or the Red Dwarf novels.

When I started looking at what's available out there that's a humor novel and Sci-Fi, all i found were fantasy novels (even the tag here is Sci-Fi/Fantasy). While I'm not against fantasy, I kinda burnt out on it.

So anyone have any suggestions of well loved sci-fi humor novels you can recommend?