Obscure but great:
Tcherepnin, 3rd symphony. Singapore symphony. BIS label.
Tcherepnin, 5th piano concerto. Singapore symphony. BIS label.
Rachmaninov, 4th piano concerto, 1927 version. Icelandic Symphony. William Black, piano.
Rachmaninov, 4th piano concerto, original vers. Ashkenazy cond. Alexander Ghindin, piano.
Myaskovsky, 2nd piano sonata. Auraphon label. Boris Lvov, piano.
Myaskovsky, 3rd piano sonata. Melodiya label. Richter, piano.
Roslavets piano music. Marc-André Hamelin, piano.
Sofronitsky playing Scriabin's 9th sonata. "Great Pianists" Sofronitsky set.
Ornstein, piano music. Naxos label. Janice Weber, piano.
Tviett, 1st and 5th piano concertos. Naxos label.
Englund, piano concertos 1 and 2.
Dvorak, symphonies #4 and #8. Excelsior label.
Brahms, piano concerto #2 played by Artur Rubinstein in Warsaw, 1960.
Mahler, symphony #10 adagio movement. Excelsior label (disc with Brahms symph #2.)
Here are a few that are not so obscure, but are great:
Rachmaninov, sonata #2 original version. Ashkenazy piano.
Scriabin, Poem of Ecstasy, Piano Concerto, Prometheus. Ashkenazy/Maazel.
Beethoven, piano concerto #5 and Pathetique sonata, Peter Toperczer, piano. Excelsior.
Satie, 6 gnossiennes and (véritables préludes flasques, pour un chien). Anne Queffélec.
Prokofiev, symphony #5. Naxos. Kuchar conducting.
Prokofiev, symphony #6. Slatkin, conductor. (I don't like the third movement.)
Scriabin, piano music (sonatas 3, 4, 5, 10). Robert Taub, piano.
Horowitz plays Mozart (sonatas).
Prokofiev, 2nd piano concerto. Ashkenazy, piano.
Rachmaninov, symphony #1. Leonard Slatkin, conductor.
Rachmaninov, piano concerto #3. Horowitz, piano. 1950s recording.
Bach, concerto for 4 harpsichords. Excelsior label.
Bach, harpsichord concerto in D minor. Gould, piano.
Bach, "ultimate organ collection". Anthony Newman, organ.
Stravinsky, Le Sacre. Stravinsky, conductor.
Poulenc, organ concerto. (I have two recordings, both good, but give edge to Previn's.)
Mussorgsky, Pictures at an Exhibition. Richter, piano.
Berg, piano sonata. Uchida, piano.
Scriabin, sonatas volume 1. Glemser, piano.
Shostakovich, symphony #15. Slovák, conductor.
Rachmaninov playing his 2nd and 3rd concertos.
Rachmaninov playing Chopin's Bb minor sonata.
Horowitz playing Scriabin's 5th, 9th, and 10th sonatas. Sony's "Horowitz plays Scriabin".
Horowitz playing Liszt's B minor sonata. "Great pianists."
Richter playing Prokofiev's 7th sonata live. Melodiya label.
Richter playing Prokofiev's 6th sonata. "Great pianists" label.
Scriabin, piano concerto. Chicago symphony.
The Hours, by Philip Glass. (Overly compressed compositions, but nice nonetheless.)
Horowitz Recital. CBS Masterworks.
Rachmaninov, the Isle of the Dead. Litton conducting London symphony.
Mozart's Requiem. Gardiner, conductor.
Lloyd-Webber's Requiem. Maazel, conductor. (Highly flawed work, but has its moments.)
Messiaen's Turangalia symphony (original version). Previn, conductor.
Complete Scriabin sonatas. Taub, piano.
The Early Satie. de Leeuw, piano.
there are many more...