This is probably too old for you, but I really enjoyed the Skylark series by E. E. Smith. It's a space opera that was first published back in the nineteen twenties in a science fiction magazine called Amazing Stories and then continued in novels until the sixties I believe. Back then these stories were amazing as they were almost like a western that was set in space, but like I said, they might be a little too old fashioned for younger readers who want blood and gore and sex and swearing in their books.

This is probably not going to help you as everyone knows the books, but the only lighthearted science fiction that I know is the The Hitchhiker's Guide to the Galaxy books by Douglas Adams. These books are extremely funny, but they contain a good dose of science fiction too as it involves our planet getting demolished by aliens to make way for a hyperspace bypass. The only survivor is a man named Arthur Dent who goes on all kinds of adventures around the galaxy after being rescued by an alien.

Everything by Harlen Ellison and Rod Serling.