1) Track that plays when Gillian heads to the factory where Gibson is. Also played in the 2nd half (after Pleasure Of Tension) of Chin Shu Oh's little speech and after Random "saves your skin". I used to think this was a SEGA CD exclusive track, but I checked and it is used in the Saturn (and I'm assuming the PSX version) during the Chin and Random scenes.
This is probably the track I'd like to get my hands on the most. That guitar intro rocks.
2) Harry's death scene track. Also played during one of Jamie's phone calls to Gillian.
3) Track played when Gillian saves Mika just before Jamie calls him at the end of Act 2. Also played just before Gillian heads out to the Kremlin (heh

If I'm wrong about any of these not being released, or you know of any others, please post about it.