i like me some sci-fi, too

ballard, of course - especially high rise. freaks me out how thin the line is... kingdom come touches upon similar themes, i'd say.
canticle for leibowitz is a great book and a must-read. after you've read ballards' portraits of apocalypse, it's always nice to read some post-apolacyptic stuff - both as cheerful, hehe

as far as PKD is concerned, my fav has always been the man in the high castle. that was my first book by him and as later found out- dealing with themes that preocuppied him his whole life - like: what is reality and what is real, so it was a pretty good starting point

a writer i'd like to recommend is a polish one - stanislaw lem http://en.wikipedia.org/wiki/Stanis%C5%82aw_Lem - the one who wrote solaris (the clooney movie is a mere shadow of the depth of the book). he's not only a great writer but also a respected philosopher.
and a nice trvia connecting him and PKD: Lem singled out only one American SF writer for praise, Philip K. Dick—see the 1986 English-language anthology of his critical essays, Microworlds. Dick, however, considered Lem to be a composite committee operating on orders of the Communist party to gain control over public opinion, and wrote a letter to the FBI to that effect.[
lol

also, there's one great story by ray bradbury that blew my mind when i first read it: night meeting

oh, and i'd almost forget: the illuminatus! trilogy - damn right!