First time I ever heard the Bruckner 8th - first time I'd even heard of Bruckner! - was in c.1960, live performance by the Los Angeles Phil. cond. William Steinberg. I was overwhelmed - and all these years later, still am. (I was thrilled to learn that a Steinberg performance in Boston is soon to appear on DVD. I shall be buying - my very first music DVD!)
CD versions that I cannot live without:
Pasido, who started this thread, already mentioned Furtwängler '44, to which I would add Furtwängler '49, rugged sonics in every edition I've ever found, but worth the annoyance.
Knappertsbusch, Berlin 1951. Yes it's the 1892 version, but so what?
Knappertsbusch, München 1962. A lot of people don't like this, they think 'Kna' had lost it by this time and was much too wandering and vague. I disagree; it's just very, very ethereal (and slow!). Again, 1892 score.
Celibidache, München 1980s. (NOT his Stuttgart one!) Slowest in history, I think - but for me that's great! Play this a few times and you will know every nuance of the score, and will have 'heard' every space between notes, which is what Celi's Zen approach was aiming for.
Simone Young, Hamburg. She uses the first edition (1887) of the score which is very, very different (incl. an entirely different ending to the first movement). Also a slow performance. Much, much better than Tintner or Inbal in this version.
Rudolf Kempe, Zürich 1971. The Haas score. The Tonhalle isn't the A-1 best orchestra on the planet, but Kempe brings out every single thing they are capable of and makes them sound in the Top 10 of the world for this overwhelming score. This is, these days at least, my "reference" recording, the one I would take to the proverbial desert island if only the island had electricity....
Yannick Nezet-Seguin, Orch. Metropolitain de Montreal. (Sorry, don't know how to do French diacritics.) Haas score. This is one phenomenally impressive young conductor with a keen sense of the inherent drama throughout every single movement; his Adagio rivals Celibidache's in both breadth and intensity. Even if you don't go buy this version, keep your eyes on this conductor, he promises very great things.
Horenstein, London Phil., c.1970. This performance has popped up in reissues over and over for years, and is essential for the 8th lover. This is Bruckner as theatre, every dramatic possibility explored to the fullest, and I know many people who would choose this for the desert island over my Kempe.
Is that enough? The above are my great loves above all; I happen to own (weird collector that I am) many, many diverse versions of this symphony, which is by far my favorite single symphonic work of them all, by anyone, except perhaps certain Haydn gems....