If you are into producing music on your computer, FL Studio is highly reccommended. This program offers countless of features! I've been using the program for about two months and still haven't tapped into every feature. The program has, by far, the easiest interface between the three top music producing programs (Reason, Sony Acid, and FL Studio). You can make anything from a heavy rock song, to an underground hip-hop beat, to and ambient trance track, to an up-tempo folk tune!
There is a little time needed to get used to everything, however, once you've got it down, the sky is the limit. After about a week of just messing around on the program you will have a good feel for it. On top of that, if you are ever stuck on something head over to YouTube and there is a good chance there will be a tutorial about your problem.
If you have a keyboard, you can hook it into your computer (if you have MIDI cables) and record your keyboard's sounds into the song! It's incredibly simple and even more incredibly fun. My friends and I have a great time making little songs on here and you will too!
Though the price is steep, www.flstudio.com has a free trial which has almost all of the same features. Try it out!