The Last Wish and Sword of Destiny, short story collections. Sword of Destiny was published first, but the stories in The Last Wish are earlier in the Witcher chronology. Only The Last Wish is published in English.

The novels:
Blood of Elves, the only book besides The Last Wish published in English.
Times of Contempt, English publication due this year.
Baptism of Fire, not published in English.
The Swallow's Tower, not published in English.
Lady of the Lake, not published in English.

Something Ends, Something Begins, a short story collection, not published in English, mostly not Witcher stories, but does have two (one is canon, the other is a hilarious non-canon account of Geralt and Yennefer's wedding).

Since you may be waiting forever for commercial translations of anything beyond Blood of Elves and Times of Contempt, check out the fan translations on the official forums.

Wonderful, i think The Witcher universe will keep me busy for the whole summer now lol.

The fans have done a wonderful job on the English translations of the books that haven't yet been given an official English translation. I've been reading them the past week. Here and there you run into some tense or homophone issues, and I'm sure that some of the color of Sapkowski's language has been lost, but all in all the translations read as though the stories were written in native English -- they have great flow and you'll have little to no problem understanding what's going on.

I was leery at first, thinking I'd end up wasting my time trying to piece together what was being said, but that was absolutely not the case.

If you're interested in the greater Witcher story, they're definitely worth checking out.

The traditional English name for a man who would lift curses, dispel hauntings, find lost objects, and so on for a fee was "cunning man". But it misses the more exciting connotations of the Slavic Vedmak, Wiedzmak, etc. A "cunning man" would be as harmless as, say, a modern chartered accountant, not a badass adventurer packing two swords.

Well, before the game was made, the most likely translation was: 'Hexer' (they translated movie title like that - but it sounded more about someone whose casting spells, not someone who wield swords)