Military Sci-fi:
Honor Harrington series by David Weber (First book: 'On Basilisk Station')
Vatta's War Series by Elizabeth Moon (First book: 'Trading In Danger')
- The person who liked the Lost Fleet by Jack Campbell, I recommend these a thousand times over as they are both top notch stories of space combat.
Gaunt's Ghosts series by Dan Abnett (First book: 'First And Only')
- Warhammer 40k at it's absolute best, certainly once you get to Necropolis and beyond. Also, first three arcs are availible as Omnibus editions which are pretty cheap for how much reading you get out of 'em.
Last Legion series by Chris Bunch (First book: 'The Last Legion')
- Only Military Sci-fi series that I've seen which features an insurrection, an alien invasion, an interstellar war, and a circus act.
Non-Military Sci-fi:
anything by Anne McCaffery
- Seriously, this woman is a master author and her Chronicles of Pern series is a pretty textbook example of sci-fi/fantasy fusion.
Aquasilva trilogy by Anselm Audley (First Book: 'Heresy')
- Another example of sci-fi fantasy fusion and a very good one as well. Sadly, no-one seems to have heard of it really, and I don't think Audley's published anything since these books.
Artemis Fowl series by Eoin Colfer (First book: 'Artemis Fowl')
- Yeah, they're kids books, but they still kick ass, especially the later ones where Artemis has grown up a fair bit.
Deeply philosophical/important:
One recommendation in here: The Memoires of a Master Forger by William Heaney. This book changed my life.