take a recording of acoustic instruments and reverse it/play it backwards
you can do it with synth sounds too, but it tends to not sound so strange and ethereal (although it can)This one sounds like it is some kinda xylophone or light bells or something.. anything with a long tail will work well.
if you want to hear some great examples of this.. check out Four Tet
here you can hear both the forward and backwards the same bit (one of my fav four tet songs)
http://www.youtube.com/watch?v=ZfflzEh9l6M
and my other favorite four tet song
http://www.youtube.com/watch?v=IuXMDhTa ... re=related