Psacanli, Well here goes - I'll try to keep my recommendations to music that I think is still in print so you can obtain it - forgive me if I fail. I'll also try to keep them to recordings that have decent+ sound.
Schumann Fantasy in C Op17 - Richter EMI 75233 (BTW did any other Schumann by Kempff in his collection interest you?)
Schubert Wanderer Fantasy - Richter EMI (Perahia's version of Sony 42124 also includes Schumann's Fantasy in C - both are quite good and its a great combo).
Schubert Sonata D960 - Volados on Sony 89647
Rachmaninov 24 Preludes - Ashkenazy London 443841
Rachmaninov Music for 2 pianos - Ashkenazy & Previn London 444845
Mussorgsky - Pictures at an Exhibition - Nothing is better by a mile than Richter's performance in Sofia but the recording is not good - essential for a collection none the less. Of other versions I'm fond of Ogawa's on BIS - excellent recording quality and good performance.
Debussy - Preludes, by Paul Jacobs from Non-such 79474. An outstanding performance and a great introduction to Debussy's music.
Chopin - so much to chose from. Rushton has already recommended many of his pieces by Moravec, an excellent choice. The only nits I would have is the recording quality can be spotty. I would start out with a set of his Preludes, Sonatas (all 3) and his Nocturnes by Ohlsson on Arabesque. I enjoy his use of a Bosendorfer and the recording quality is quite good.
Beethoven - For a set of all of his sonatas I would select Goode's set on Nonsuch - excellent recordings and performances (I have all but a few from when they were issued individually.) For individual pieces the one that I come back to most often is #29, the Hammerklavier by Gilels on DG.
Brahms Sonata #3 etc If you can find it I highly recommend this piece by Kubalek on Dorian - in addition to the Sonata the includes 16 waltzes and the most beautiful 3 Interemezzi op 117. Curzons #3 on London, and Perahia's on Sony are excellent performances and probably obtainable. If you're ever up to a complete set Julius Katchen on London is a complete winner.
Lizst - Sonata in B (recommended by Rushton) is outstanding and a big piece. The Reference Recording is great sonically. For something more lyrical, and for me anyway, more endearing and enduring, is his complete set of Annees de perlerinage by Lazar Berman on DG 471447. If you don't want to spring for the whole set (3cd's) get Primiere annee Suisse - Jorge Bolet on London is excellent as are most of his recordings of Liszt.
Hope that helps a bit. If you want more let me know which composers attract you most.
Liszt -
