If we provide too many more examples, Wunja will be back to square one (but that's not going to stop me).
I guess one thing to consider Wunja is whether you want to ease yourself in to Science Fiction, or are you looking for 'classics' of the genre, looking for what possibilities it has to offer etc.
To ease yourself in from more familiar literature I would recommend
The Dispossessed by Ursula Le Guin. It's an accessible read but is literate by non-genre standards and contains some thought provoking political ideas. One of my favourite books of any genre.
Many (but by no means all) of the classics of Science Fiction originate from cold-war era American writers. As others have said, Ray Bradbury, Philip K Dick and Robert Heinlein among others have produced some of the classics of that period and are worth reading if that is what you are after. Personally, while
Fahrenheit 451 (Bradbury) and
Stranger in A Strange Land (Heinlein) are both regarded as classics of the genre, I personally found both to be a little overrated. Reading them now may not be the best introduction to what the genre can offer. On the other hand I think Philip K Dick has produced some masterworks. As an introduction I'd consider
Time Out of Joint or
Ubik as typical of his mid-period stuff. If you like it, definitely consider his some of his later and more ambitious works such as
A Scanner Darkly,
VALIS, and
The Transmigration of Timothy Archer.
As for more modern
SciFi SF that uses the genre to explore form of writing among its themes, I'd second the suggestion of
Feersum Endjinn by Ian M Banks. While a quarter of the book is written in phonetic English (as the title), it is surprisingly readable and a good introduction to Banks' science fiction work.
I am no expert in
SciFi SF (case in point) and generally find 'difficult' literature, well, er, difficult. But one of the problems with it as a genre is the huge volume of trash. For example, while I loved Harry Harrison's Stainless Steel Rat books when I was 14, in my view they are just that - books for 14 year olds (hiding behind a respectable veneer of pastiche).