Joe Haldeman (Sci Fi) - The Forever War, 3 books (I think) easy reading and good action, believable portrayal of long term space travel and the effects of relativity.
Harry Harrison (Sci Fi) - The Stainless Steel Rat series, very good Thief turned Investigator type stuff.
Issac Asimov (Sci Fi) - Foundation series.
Arthur C Clarke (Sci Fi) - Rama series. Also, get the Collected Short Stories, they are all in one (big) book, some really good stuff in there.
Stephen King and Peter Strawb (Sci Fi/Fantasy) - The Talisman.
Julian May (Sci Fi/Fantasy) - The Many Coloured Land, 3 books (I think). People who chose not to fit in with society choose to be sent back to the Pliocene epoch on a one way trip. Good stuff!
There's lots more, in my loft, under the bed, on bookshelves, bloody everywhere. Ive been buying books (mainly Sci Fi) since I was about 8, and never sold or thrown any away. The wife has threatened to give them away, I told her I'd give her away first!!