I am only into 20th century classical, almost exclusively music from post WWII, to the present, which I know not everyone's cup of tea, but I will certainly take part in this thread.
I'll start with the recording that really spurred my interest in classical music.
Ernst Krenek - Static and Ecstatic / Kitharaulos
Not only do I love this from a musical standpoint, but the vinyl recording has a large, deep, open soundstage. It is one of those soundstages, that can fool you into thinking you can walk among the the musicians.
There is also a much more recent recording of this piece by the Cleveland Orchestra.