Try Holst's Egdon Heath - it has the same other-worldly element as Saturn and Neptune.

Here's a fragment from Stravinsky's Frankenstein Suite:

http://www.youtube.com/watch?v=iTscRFiDTos

They really knew how to create a scary television programme in those days. Hear the little boy scream: "Let me go! No! Mister!"

I think I'm going nuts - I could have sworn someone mentioned Scriabin but I can't find it now - maybe nobody did.

In any case, Scriabin is often listed as a prime synaesthete because Prometheus was first performed accompanied by a light show (originally I think he had an instrument that was meant to project the colours as they were played) that was theoretically based on his "coloured hearing", although that in itself has been subject to debate.  His spectrum of colours seems too ordered and complete, ie he's got pretty much every colour of the rainbow in there and it comes across as too thought out and artificial rather than spontaneous, as though he's starting with the colours and trying to find somewhere to slot them in.  As it happens, Scriabin slated Rimsky Korsakov, implying that his synaesthetic interepretations were association-based, although to me looking at their two charts, Rimsky-Korsakov's looks the more genuine just on the basis that it's a bit more arbitrary.

Richard Cytowic's "The Man who tasted shapes" is a good read.