As I'm in college, I don't have summer reading, but I did pick up an armful of books from my dad's shelf, all of which come highly recommended. If you like reading, take a glance into a few of these.
A Talent for War - Jack McDevit
Part of the Alex Benedict series, a very well written science fiction novel. Think Indiana Jones in space. He's an artifact salesman who gets himself in a bit deeper than expected.
Starship Troopers - Robert A. Heinlein
What started science fiction. If you've seen the movie and hated it, you'll love the book. They're nothing alike. A rather short read, good for airplane or car trips.
Variable Star - Robert A. Heinlein and Spider Robinson
Possibly one of the best books I've ever read. Another science fiction involving traveling to a new world for the first time. The way Robinson describes music is fantastic and probably one of the most fluid books I've ever read.
Dies the Fire - S. M. Stirling
Are you afraid of the dark? What would happen if electricity and gunpowder suddenly stopped working? Without your modern day tools and equipment, could you survive from day to day? Dies the Fire is an interesting book, striking at the idea of "what if" the general pressure of the earth were to change by a few pounds, disabling electricity, steam power and gun powder. I can't say suggested read, just because there's some stuff in the book about Wicca [a religion involving witchcraft] and some people just don't go for that sorta thing.
Into the Looking Glass - John Ringo
Haven't read it yet, a science fiction book that seems like it's similar to Stargate, except the badguys control all of the stargates. From the excerpt I read, it seemed somewhat bloody.
Rainbow Six - Tom Clancy
I read it a LONG time ago. Basically it's what created the R6 games. It's what started the entire genre of counter terrorists saving the world from terrorists who have some bio weapon or nuclear weapon. Very well written.