It sounds like your reading habits are much like mine. I have great difficulty reaching beyond the known authors and series, very probably to my detriment.
Here's my go-to list because I'm too damned stubborn to change:
Historical fiction series
* Dudley Pope's Ramage series (Napoleanic wars, nautical -- think Sharpe's Rifles, but on the water and not quite as light)
* Dorothy Dunnett's House of Niccolo series and Lymond Chronicles
I should note: There's much swash to be buckled in all three of the above series. Dunnett's, especially, has breathtaking moments and your heart will break a bit and then be rebuilt by many of the characters.
* Bernard Cornwell, pretty much anything. The Archer series is good, and of course Sharpe's Rifles, etc. It's lighter reading, compared to most of my list, but wholly enjoyable. The title escapes me, but he has one about Stonehenge that I found fascinating.
* Ken Follett, in particular his duo Pillars of the Earth and its sequel. He's written some WWII-era series as well, but my attention is generally kept by the medieval-era books. They're beautifully-written dramas.
Science/Speculative Fiction
* Anything by Iain Banks (spec) / Iain M. Banks (sci-fi). Anything. Every damned book. He's amazing.
* Ditto Ursula K. LeGuin. Her books and stories have made me sob with the hopelessness of it all, then turned right around and inspired me to do better and see the world as full of possibilities rather than obstacles. There's a collection called The Word for World is Forest, titled after one of the stories it contains, which does that to me every time I read it.
* K.J. Parker, and I would recommend you start with the Engineer Trilogy. (This author I categorize more like speculative history, by the way.) There's not a single person in any of her (I'm assuming KJ is a female, it's a hunch, and there's great mystery about it) books wholly innocent and endearing. The characters are portrayed as difficult or damaged people, enduring difficult times, making difficult decisions. The psychologies are extremely well-written and the stories are compelling. My favorite independent, non-series book is The Folding Knife, although The Company was mind-blowing.