One of the first--and most fun!--science fiction movies I've ever seen is Roger Corman's Battle Beyond the Stars.
Shad (Richard Thomas) sets out to save his tiny home world of Akira from John Saxon's aptly named Sador! Shad steals a slightly clingy spaceship and gathers a ragtag band of fighters to help. I was thrilled with George Peppard's space cowboy. Robert Vaughn's mercenary is an amazing reprisal of his Magnificent Seven role.
Fantastic space battles, cute humor, and wonderful performances by a really fun cast.
"Live fast, die well and have a beautiful ending!" -- Saint Exmin, the Space Valkryie