I read pretty omnivorously, but science fiction, nonfiction science, and history draw my interest the most.
Dumarest of Terra, a.k.a. The Dumarest Saga is a series of over 30 books written by E. C. Tubb.
I consider the first book in the series a must-read classic of SF, even if you never read any of the others.
The idea of starting a 33 book series can be daunting, especially when most of them are only available used. I've written an overview that covers the ins and outs of it, as well as individual reviews for the books I've read so far.