Speculative Fiction Starter List:

1. Robert A. Heinlein: The Moon Is a Harsh Mistress
2. C. S. Friedman: This Alien Shore
3. John Ringo: There Will Be Dragons (The Council War)
4. Elizabeth Kerner: Song In The Silence: The Tale of Lanen Kaelar
5. David Drake: Redliners
6. Elizabeth Moon: Remnant Population
7. Spider & Jeanne Robinson: The Star Dancers
8. Lois McMaster Bujold: The Vorkosigan Series
9. Orson Scott Card: Songmaster
10. Anne McCaffrey & S. M. Stirling: The City Who Fought (Brainship)

Focus for this list:
Each of these books is a stand-out in its particular sub-genre, and they're all wildly good reads. Think of this as a variety box of truffles; not all will be to your taste, but they're all high-quality and stand a good chance of getting you hooked!