While a lot of the sci-fi that I review or share on here is rather deep. There are a lot of things that you can do with the genre. And humor is definitely one of them.
"John Dies at the End" by David Wong
I would be more tempted to say that "John Dies at the End" is actually more horror comedy than sci-fi than anything actualy seen as true sci-fi. The novel stars John and Dave, who ended up being drawn into the strange and horrifying paranormal craziness of their unnamed Midwestern town.
When you are done with this book you’ll never look at soy sauce the same way again.
"Redshirts: A Novel With Three Codas" by John Scalzi
This one is most definately sci-fi book. And a wonderful one at that. If you have any exposure to Star Trek you will be pleased with the tounge-in-cheek adventures Ensign Andrew Dahl as he tries to stay alive while accompanying the starship Intrepid's bridge crew on increasingly more dangerous away missions to alien worlds.
trope of the original Star Trek series, Redshirts follows
"Hitchhiker’s Guide to the Galaxy" by Douglas Adams
Seriously, if you haven't read Hitchhiker's Guide to the Galaxy, stop what you're doing right now and go pick it up. A fantastic, comedic read about a poor hapless human named Arthur Dent as he traverses the odd corners of the universe with alien explorer Ford Prefect, this novel is just a flat-out entertaining read and a must-have for any sci-fi fan.