A few years ago, the Mystery Guild book club published a book called "Queen's Ransom," featuring three quite good and quite representative novels by Ellery Queen. As far as I can tell, the volume is the only collection of Queen novels still available in print.
Still, if you're a Mystery Guild member, or interested in becoming one, I'd suggest you check out the book because it includes the very first Ellery Queen novel: The Roman Hat Mystery. First published in 1928, it introduced Ellery Queen - the detective character and the author - to the world, along with his father, Inspector Richard Queen, and some of the other regulars who inhabit the Queen novels.
It's a good, solid mystery - a man is murdered in a Broadway theater. He is fully dressed in evening clothes, but his top hat is missing. Is that significant? Ellery Queen says it is - and he's right. It's an impossible crime situation and also a thoroughly fair puzzle, complete with a formal challenge to the reader to come up with the solution before Ellery explains it.
It's a fine introduction to one of America's greatest Golden Age authors.