google Reaper. it's freeware or you can pay if you choose to follow thier request. i think it's gone up recently to either $50 for personal use or $200 for commercial license. comes with a good variety of packaged plugins and works well with many other free/pay plugins.
many users swear by it (me being one of said users).
I'm using GarageBand on my Mac for laying down ideas, but of course you need a Mac for that. I have an MBox 2 and Pro Tools LE that I haven't really gotten into, and since have decided to go a different route. I am now using Logic Studio as my main software. You can't really go wrong with any of them, but make sure it is compatible with your setup. I'd look into Pro Tools, Logic, Cubase, Nuendo, Sonar, etc. and find one you really dig.
Pro Tools is the industry norm, and I personally feel it is pretty easy to use, so that is probably what I'd recommend, that or Logic 8 (Express if you're on a budget). If you need an interface and Pro Tools, PM me; selling the MBox 2.
P.S. I play with Paul in the Jason Turner Band.
I am selling the MBox and Pro Tools if you're interested.