I started with Fruityloops about back in version 2.5 up until 4.3 or so. It was alright, and fairly compact so a quick download.
What really has has me obsessed in the past year and a half is Reason 2.5. It's more geared towards electronic music and people who buy rackmounts full of drum machines, analog synths, mixers, etc and link them together. The entire interface looks like one big rackmount on the front, and the back panel screen looks like all the same wires and setup you need to plug/unplug on a full setup.
It comes with some fairly powerful synths, the song composition/mixing is very well done, and it looks so similar to popular hardware that after you've been playing with it for about 2 months, you already know how to put together a sound studio with real equipment thanks to the sweet graphical interface.
It's about 3 cds and released by Propellorhead. Refills and sample kits for it are fairly plentiful on p2p networks, just search for *.rfl.
I also suggest a good copy of Sonic Foundry: Soundforge wave studio for tweaking individual effects/compression on wav files you want to import to the program, and SOnic Foundry: Acid for some decent sound mastering/mixing of your track files after your done building and exporting them from Reason 2.
Those 3 programs pretty much do the same things that several thousand dollars worth of physical electronica equipment and then some. Sure it'll never be as fun to play live as an Xbass 909 or a Korg Triton, but you can make a finished track sound just as good, if not better sounds quality than hardware. Also, Reason is very compatable with Midi Composition and having external keyboards controlling instruments live, and unless you're running something like the last surviving PII 400mhz, it'll play very fluently and clean.
Again, the best part about Reason is how close the interface is to working with real and expensive equipment. After you make 3 or 4 songs with it, you can walk into Sam Ash Music and spend hours in the electronics room making actual music rather than aimlessly flipping panels and making noise. You can pick up any synth and know what each envelope and frequency sounds like, or program a drum machine with 20 patterns in less than an hour.
I never really got into Cubase, Sonique or ProTools that much. Their interfaces give me a headache and everything looks like a silver alien control panel.
