@BrandonInOhioPicking JUST one is nearly impossible - depends on audience, context, mood etc... Depending on the preference in taste of crayons, here's some possible options for you:
- For "Star Was" nerds, any Zahn books in Star Wars EU featuring Thrawn. They were the height of SW franchised books, and haven't been surpassed even by now despite their age.
- If you like technothrillers, Tom Clancy's "Jack Ryan" series (actual Clancy, not garbage ghostwritten with his name after he died) - starting with "Hunt for Red October" (yes, the Sean Connery movie was based on that book - in total 4 of the books in the series were made into movies, 2 great and 2 crappy).
- For SciFi, "Dune" series? Or pretty much anything by Greg Bear.
- For space opera subgenre, anything from David Weber, but my fave is "Dahak" series (aka "Empire from the ashes"). "Honor Harrington" series is always great (and with tons of books - think "Horato Hornblower" in space), "Safehold" is also good though quality dropped a bit in later books.
- For alt hist/time travel, Eric Flint's "Ring Of Fire"/"1632" series is pretty amazing. While on Flint, his debut book "Mother of Demons" is amazing and "Pyramid Scheme" is a must read for anyone with a sense of humor and even a passing interest in Greek mythology.
- For general SciFi, Card's Ender series (started with "Ender's Game" obviously; but personally I like "Ender's Shadow" even more and the rest of Shadow arc).
- If you want more old-timey classics, can't go wrong with Duma's "The Count of Monte Cristo".