Music creation for SoM games

[Verdite]

Does anyone know of any decent free and easy to use software that i can dl to create some interesting music for my games? I've already got alot of music lined up, but some of it doesnt fit entirely... I loved the old KF music, pretty much all of it was great (except some which was almost too dark.)

I'd like to mess with synth, keyboard keys and some ambient sounds.

Thanks

Verdite