Good question!

Myst 3 and 4.
Gabriel knight 3 also had wonderful music!


and.... Dreamfall as well!

The strange thing about the Syberia games is that I didn't notice the soundtrack much when I was playing the game. I remember the menu screen music, and some of the music when cut scenes played, and Helena's aria, but I don't remember much in-game music otherwise.


The trouble I have with Ring's music is that it isn't original. It's using previously written music from Wagner's Ring cycle. So it isn't really what I think of as game music because it wasn't composed for a game. It wasn't even gathered from separate sources, like Faust's music was.

The Myst creators give a lot of love in the music part of the series... that's for sure...

Shiver's 1
7th Guest/11th Hour (actually has CD to purchase by The Fat Man and Team Fat)
Myst 1
Phantasmagoria

are my picks,
Shelly

I loved the soundtrack in the Gabriel Knight games. It was perfect. Also, the soundtrack in the first Broken Sword games fitted the mood and style of the games. I think the best soundtrack is that which you don't recoginze much because it kinda stays in the background. It just contributes to the atmosphere without becoming dominant.