Quite a few good ones already mentioned. If you want a sci-fi or fantasy book you are already well-covered although there are many others that deserve a mention;
Iain M Banks for sci-fi - try the Player of Games or Use of Weapons as they are very much standalone novels.
China Mieville for fantasy - try The Scar
If you aren't after such dense reading maybe something a bit more fun - grab Slaughterhouse Five by Kurt Vonnegut (its sort of a war novel, sort of sci-fi with a splash of comedy).
Iain M Banks for sci-fi - try the Player of Games or Use of Weapons as they are very much standalone novels.
China Mieville for fantasy - try The Scar
If you aren't after such dense reading maybe something a bit more fun - grab Slaughterhouse Five by Kurt Vonnegut (its sort of a war novel, sort of sci-fi with a splash of comedy).