I see John Ringo
has been mentioned and I'm glad. He is my current favorite SF writer as he's both humorous and
deeply stimulating in his writing style. For instance, his "Legacy of Aldenata" series explores the concept of an alien invasion by a species that
is barely sentient and ravenous in their quest for resources and "food" with a twist of other "aliens" aiding humans because humans are so violent
compared to other species of their little corner of the galaxy.
Another good series by him is "Council Wars" series which looks at a future utopia where humanity has pretty much become gods because of their own
technology and what happens when we suddenly lose their power. Excellent series that successfully combines Science fiction with a fantasy overlay.
David Weber is another of my favorites with is space opera "Honor Herrington" novels. Great space battles and pretty good science behind his works