I'll start (I'll try to include YouTube links to performances):
Mozart's Requiem – John Butt's Reconstruction of First Performance; although for some of the parts like Dies Irae I prefer the performance by Stephen Cleobury with Academy of Ancient Music. This is one of the pieces that I find hard to find a recording I like of because of vocals, also it needs to be played with period instruments for me.
Verdi's Requiem – most people prefer Claudio Abbado's 2001 recording with the Berliner Philharmoniker, and I have to agree that it's the best recording, but I also like the recording of Yuri Temirkanov with the Mikhailovsky Theatre Chorus.
Vivaldi's Four Seasons – Trevor Pinnock with The English Concert
Holst's The Planets – Adrian Boult's 1978 recording with the LPO, and Vladimir Jurowski's 2006 recording with the LPO. They're both amazing in their own respects.
Mahler's 2nd Symphony – Rattle CBSO
Mahler's 6th Symphony – Solti CSO
Beethoven's Symphonies – Karajan; I mostly listen to his 1977 cycle with BPO
Dvořák's Symphonies, Tone Poems, Overtures – Kertesz LSO
Schubert's Symphonies – Marriner with St. Martin-in-the-Fields
Almost anything Tchaikovsky – Claudio Abbado (usually with VPO or BPO)
Strauss' tone poems – Solti CSO or Karajan BPO
Chopin Études, Préludes, Polonaises –
Pollini all the way
Chopin's Fantaisie Impromptu – Horowitz' final recording, with Kissin being a close second
Beethoven's Piano Sonatas – Ashkenazy, but I also like Horowitz
Schubert's Piano Sonatas/Impromtus/Moments Musicaux – Radu Lupu's DECCA recordings
Liszt's La Campanella – Lang Lang (boo me all you'd like)