Robert Heinlein is the best! But besides him Gamer5 basically covered the best authors of our time. Would recommend reading at least one work of all.

Edit: I just remembered another few good writers
Ursula Le Guin. Like Heinlein she (not so) subtly addresses the ills of society and possible solution and scenarios as well as their hypothetical outcome. You should defiantly look her up.
Aldous Huxley - One of the best Dystopian writers of our age, Huxley wrote such novels as Brave New World, Crome Yellow and Island (Which i am reading at the moment and is surprisingly Philosophical even for Huxley). If your not into deep meaningful plot lines that reflect humanity I would still recommend Brave New World as its worth at least one read and has one of the most memorable endings i have read.