That depends on which genre you are interested. Czech writers cover a large amount of different genres.

The number one best writer is considered to be Karel Čapek ( Č is pronounced the same way like CZ). He covered a wide variety of topics. For me personaly the best thing he wrote is the theatre play R.U.R. ( Rossum's Universal Robots), which later inspired Isaac Asimov's stories.

Czechs are also famous for their, often dark, humor. One of the best best examples is Jaroslav Hašek and his novel The Good Soldier Švejk. Imagine that you live in a world after the First World War. Many have died, the guys like Hemingway and Remarque are writing, how the war was a hell. And then some dude from Czechoslowakia releases his novel about the Great War, but it isn't the same brooding and dark stuff like the writers before. On the contrary he made fun of the war and the whole fighting. No wonder this novel holds a record as The Most translated Novel of Czech Literature. Bonus points if you manage do get the version illustrated by Josef Lada, but that could cost you a pretty penny.

There is a lot of other great writers, but I think that this is enough for now. Our culture has a lot to give to other countries, but we sadly weren't able to "market" it like for example Japanese.