Stanislaw Lem for the most philosophical and probably most intelligent SF there is.
Also, read it for the insane amount of puns. (The Kandel translation is excellent.)
Also, because they're a bit older, for the goddamn charme of old SF technology.
The Invincible (http://en.wikipedia.org/wiki/The_Invincible) is probably his most "classic" SF novel.
The Star Diaries (http://en.wikipedia.org/wiki/The_Star_Diaries) is a series of stories centered around a traveller named Ijon Tichy. Ramps up the bizarre. Includes one story where time fuckups end with Ijon beating the crap out of himself for being such an unreasonable jackass. Fucking awesome, all of the stories.
Tales of Pirx the Pilot (http://en.wikipedia.org/wiki/Tales_of_Pirx_the_Pilot) is less bizarre, more hard SF, more grimdark-while-sort-of-funny. Includes fucking up first contact due to a tape machine running out of tape due to space travel being like the Russian merchant navy.
These are the three main things I'd recommend you. Anything else, go for it. Lem is uniformly awesome, and he's the most underrated SF author I know of. But it's not exactly light reading, what with him getting heavily into philosophy and shit at times.