Propellerheads "Reason" is one of the best applications for creating music and sound fx, however it's not as simple and easy to use as FruityLoops. But, there's a free demo version available on their website.
If you want to be able to use instruments you can download (VSTi) then you want something like FL Studio or Cubase. If you want something that is a little more tightly integrated and more like a packaged studio, go for Reason 3.0. Reason is very good but it's limited in that you can't use VSTi plugins. Your choice of sound expansion comes down to samples and that's it.