Use of Weapons,  Banks.
The Moon is a Harsh Mistress, Heinlein
Armor, Steakly  (sp?)

I will submit my three before reading the other responses.  I'm going back like thirty years from memory.  I may edit after...

From the last six years:

1) the Windup Girl.  Almost post-apocalyptic, very near future sci fi.
2) One of the Hyperion books.  I can't remember which.  
3) Leviathan wakes


From my readings in the 80's and 90's:

1) Ender's game
2) Battlefield Earth
3) The Peace War

Books that had too much New World Order/Liberalism but were memorable:

1) Xenogenesis trilogy
2) Venus of her dreams
3) Ringworld series after book 1


Best sci fi series:
1) the dragon riders of Pern--especially around the time of  the White Dragon.

SHORT STORIES:
1) "sixth of the Dusk" by Brandon Sanderson, found in the "Arcanum unbound" collection.

I'm reading Leviathan Wakes now- it's pretty good for sure.

Pern is fantasy isn't it?

Leviathan Wakes was a sale book on audio--and my re-introduction to sci fi after not reading sci-fi/fantasy for almost 20 years.  it blew me away.  I was surprised.

Pern starts as fanatasy but morphs into sci-fi by Dragonquest and The White Dragon--I believe these are the original series, books 2 and 3.

Oh cool, my sister was always really into them but I haven't read them. Blend of sci-fi and fantasy can be good.

If you like that sort of thing, check out Mistborn- it's fantasy right now, but the last trilogy (unwritten as of now) is going to be a blend also.

Love first three Mistborn novels--mind blowing.

Did not like "alloy of law" series as much.

Anne Mccaffery really did the sci fi fantasy blend expertly in dragonriders books.

Right?! I loved them too. THe next trilogy is going to be an 80s cyberpunk Mistborn, then far future sci-fi in the Mistborn world...I have high expectations.

I suppose I will need to break down and check out Pern.

Starship Troopers
Cosmic Computer
Hammer's Slammers

 
A friend has a book that is effectively priceless - limited edition hardcover of one of the Pern books,  something like number 8 out of 20, signed by Todd and Anne.  I'll see Todd next weekend,  he's volunteered to cook breakfast :)

Dune Series.
The Dosadi Experiment by Frank Herbert
The Forbidden Borders Trilogy by W. Michael Gear

1. Dune
2. Battlefield Earth
3. Can't remember the name, it was about a space cowboy with a robot horse on backwoods planets.

Cool stuff. How'd it go?