There are a lot of options depending on what you want to do, how much you think/implement in code, and the level of complexity you're ready to opt into...the more complex, usually, the more control you have when you're tackling the tricky bits (talking to homebuilt MIDI devices, sensors, sonifying realtime data, etc.)
Here are some of the other packages you might want to check out.
cSound is a classic if you're not afraid of code. Max/MSP/Jitter is more graphical and insanely powerful. Pd (pure data) is an open source take on the Max/MSP paradigm. Reaktor is a more commercialized, easier-to-use, but maybe not-as-powerful modular synthesis/sequencing environment. U&I Software's famous Metasynth software can be sequenced with its companion product, Xx, for a very different kind of graphical computer music experience.