Started out as just a software drum machine but has evolved into one of the best pieces of music ware that I've seen. Also check out SimSynth which is an Analog Synth emulator. Download the demos, then buy the products. Great utilities and software. Take me there Propellerhead Software Makers of Reason, ReCycle and ReBirth.
Reason is a complete virtual studio.
You have to see it to fully appreciate it, but it is absolutely astounding. ReCycle allows you to chop up samples and loops and then import them into your favorite sampler for remixing, And ReBirth is a software reproduction of the staple sounds of the techno arsenal. They offer a demo for download on their site as well as sample songs written by various artists using ReBirth. Way better than having to futz with the tiny LCD display on the synth. Definitely worth the donation.