In most any digitally produced music synths are needed. They can give an ambient background noise, or a trembling trance lead to get that crowd going. Among my favorite synthesizors are prism and reaktor by native instruments. Those are very serious artificial synths though, if you want something just to play with FruityLoops Studio is my go-to guy again. in the OtsX instrument package, you can find ambient and trance lead instruments, and they never let me down. By adding effects or automation, you'll have a song going in no time.
Another thing to play around with is Sytrus, an input instrument in FL Studio. It has packs of anything you can think of from growling, to raindrop piano. I highly recommend it.