With the recent popularity of the movie "Shine", Rachmaninoff's 3rd piano concerto has gotten some more attention.  The David Helfgott recording is sitting in mass quantities on the shelves of all record stores, but really, it leaves much to be desired.  There are actually several mistakes, and you don't quite have the overall sense of "oh my god" when you hear it.  To achieve that feeling, I reccomend the Byron Janis recording of it.  It's flawless, and SO powerful.  This pianist has POWER.  He was a student of Rachmaninoff's so his interpretatation of the music is just as the composer would have intended.  There is also a recording of Rachmaninoff playing all his piano concertos himself.  The recording quality is naturally rather poor, since its from the 1940's, but the man plays like he was possessed.
    There is actually a series of recordings called "Rachmaninoff plays Rachmaninoff".  Any fan must hear these recordings.  Rachmaninoff was not only a fantastic composer, but an incredible pianist....really  incredible.  There is even a CD called "The Ampico Recordings" which used some piano rolls that were made by Rachmaninoff on a player piano type mechanism while he was still alive.  These rolls were then fed into a new piano in the 70's to get a quality recording of Rachmaninoff's playing.