It's an Organ preset patch of the Casio CZ101/1000. Haha, one of the first synths I ever bought and instantly recognised that sound from some Rave type tracks.
Here's the sound 1:15 sec into this youtube vid:
http://www.youtube.com/watch?v=W6vyCNWJVME
[edit] Should have read the replies first, it's been answered.......