Now you've done it. There's so many SF fans here that this thread will grow and grow.
Here's my recommendation: Alistaire Reynolds "Revelation Space" He's a PhD physicist and does a very good job of weaving current trends in cosmology with and intersting premise why we are apparently the only intelligent life in the galaxy.
That series is very good. But it must be read from the beginning. A friend of mine picked up book 3 by accident and found the whole thing completely incomprehensible. Even if you start from the beginning you are expected to use your head to work out what is going on.
Quick summary of the Sci-Fi books' recommendations: (in no particular order):
Alistaire Reynolds "Revelation Space" (must read from the beginning)
The early Honor Harrington stories by David Weber.
Peter Hamilton's Reality Disfunction series. Peter Hamilton's Pandora's Star series.
David Feintuch's Hope series. (first 4 books)
Heinlein
Forward
Niven
Pournelle
Joe Haldeman
Keith Laumer's time travel and alternate-universe stories.
Iain Banks "Culture" novels
Greg Bear (Eon, Queen of Angels)
Neil Gaiman (American Gods, Good Omens-with Terry Prattchet).
Vernor Vinge (everything),
Dan Simmons (Hyperion Cantos)
Neal Stephenson (Diamond Age and Snow Crush)
Orson Scott Card