Star Wars: Death Troopers. For once it's not about any jedis, and you have zombie stormtroopers. I mean sure, zombies may be a bit much lately, but honestly: Zombie Stormtroopers. They can't aim for crap, but there's so many of them and now they're hungry for flesh.
Halo Series (I have read all but the newest one about the old race that invented the flood), the games may not be amazing, but the books are actually all well done. Especially Contact Harvest was my favorite of the entire series. And that's saying something when you have Reach and First Strike to choose from.
StarCraft books, at least the Terran ones I've read. Ghost was horribly depressing and I somewhat regret reading it, but still an interesting read. Heaven's Devils is my favorite about Jim Raynor when he was younger and full of life. Another decent one is I, Mengsk. Shows the downfall of an otherwise amazing Mengsk could have been to bring about a new era of peace for the ravaged StarCraft legacy.
Gears of War books as well. They're for the most part slow paced and allows a view into civilian life and the depressing fact of how people are living in the world.
Of course I'm sure many have already listed Starship Troopers, Hitch Hiker's Guide to the Galaxy, Fahrenheit 451 and the like, so I don't really have to explain those. Anyways, you can't go wrong. Just go read the first chapter or so of each book that people list here and see if it catches your eye. I know some online services allow you to read a chapter or two online. Go expand your knowledge and have fun!