as far as sci/fi, fantasy:
have you checked out the robert jordan wheel of time books? i know they're really popular now, but they're quite good, if a little overly descriptive. and there's enough there to keep you reading all summer...
try guy gavriel kay's finevar tapestry. one of the best fantasy books ever written, i'm certain.
how about four lords of the diamond by jack chalker? very good.
regarding NOT fantasy/sci-fi... i always like to recommend one of the writers from 20th century america who is vastly underrated... john fante. he was very inspirational to bukowski, among others. check out "wait until spring, bandini", or "ask the dust"... both extremely good books.
i also have been on a classics kick in the past year, and if you haven't read it, go buy "a moveable feast" by hemingway.
a recent writer who my big bro sold me on is michael ondaatje. he wrote "the english patient" but "in the skin of the lion" is amazing and my bro says "coming through slaughter" is even better...
there, if you've read all of those, get back to me, and i'll think of something else!