Propellerheads is also a software company that makes awesome electronic music tools. They make Rebirth, Reason, and ReCycle.
Rebirth is an emulation (Yes, emulation, not simulation) of the three synthesizers that basically started rap, techno and other electronica; they are the Roland TR-808, 909 and 303. The 808 is mentioned in the Beastie Boys' "Body Movin'": Nothin' sounds quite like an 8-0-8. It is a lot of fun to use, I only have the demo version, and I feel like a genius when I play with it.
Reason is an emulation of samplers, synthesizers, sequencers, and other effects that are used to make techno or hip-hop loops. I've never used it, but it is designed to be very flexible. Need another sampler? Just put another one in. It's very cool.
ReCycle is a loop re-use tool, for taking loops and playing with them or editing them for use in other tools like Reason or ProTools or GrooveMaker or stuff like that.

Their stuff is really well done. I want to use it more than I have.