Garageband. This program can be considered a "begginners" program or perhaps a "recording" program rather than a program for making music. I, however, consider it a "Creative" program. It can be used to make music at... a very different level. Many assume that it has limited features with barely any interface for making synths from scratch. Many abuse it and make music with the ever dreaded loop library, which is really there for lazy ass production guys who want to use non copyrighted music in their commercials or for grabbing easy to edit beats for songs.
HOWEVER, once you dig your dick deeper into this program, you will realize that its a bit sexier than you might have thought. This program has two very key features that make it just as good as fruity loops or many other programs out there. It can load in external and internal midi inputs and outputs along with support for thousands of VSTs, Plugins, and Audio Units. The great thing about the mac is that practically all of these great plugins are absolutely FREE. And hey, if your that much of a cheap ass, then just go and pirate Reason or something... or better yet pirate the plugins... besides I highly doubt that you won't be able to find a free version of whatever plugin your looking for. I have found nearly everything there is to be needed on this simple site. It has millions of thingymabogers for making music. Check it out.
Anyway, I recently have been using Garageband to make all of my songs. Garageband makes the import of VSTs (audio units) and Plugins flawless and easy to record. I can be really fucking creative with recording techniques. Right now, I am able to make whatever I want with just a few easy to use plugins that I dragged and dropped into my audio folder.
So yeah, Garageband is a fucking awesome host. Its like a bitchin fraternity guy throwing a party, inviting all the cool and awesome plugins to dance on the dance floor, get topless, bring beer, and make the party awesome.
Here is just one plugin I put into it.