The best Remix is the Deep Tunnel Remix by RadiuZ!
The Castle Bosslevels in a Houseremix.
Machinae Supremacy Metal Version that is also used in Twisted Dreams.
The Classics Collection
The C64 SIDs in quite good soundquality.
Hall of Fame Music @ 3:37 - Level Music @ 5:24 - Main Screen Music @ 7:05
The same in an orchestrated version.
Recorded by the WDR and called Symphonic Shades.
You can also download the Giana Sisters Soundtrack as mp3s
I don't offer the Symphonic Shades for mp3 download here, you can get it from all online music stores.