Beat making programs
Hmm, I don't produce rap but production wise what I do is fairly similar.
My toolchain is as follows: ReCycle for loop chopping Ableton Live 5 or general sequencing/remixing NI Traktor if I'm ever forced to DJ.
If you're interested in which synths/keyboards: Synths: SoftPlug AdventusDF, RCG Z3TA+ and Synapse Junglist A Korg Polysix and Wavestation Mastering: ElementalAudio Equium and Ableton's saturators/compressors and EQ tools.
Highly recommend the RCG z3ta+ soft synth, and the NI Pro-52 if you can get it.
I'd say if you're just starting out just get Propellerheads Reason 3.0, it's basically a virtual audio production rack, you get mixer, drum computer, synths, samplers, even a vocoder, and loads of effects, reverb, DDL, chorus, phaser, compresser, eq, etc. There are tons of preconfigured drum kits to load into the ReDrum computer (some hip hop ones too) and even loops for you to play with for the Dr. Rex, or u can make up your own kit from the individual drum samples, and there's tons of nice meaty sounds for the synths to make basslines out of, etc. Oh, and on top of all that, v3.0 now has a built in mastering suite :)
I'd recommend getting that first and then adding to it later as the need for specific tools arises. It's pretty much an all-in-one kit. You can always add to it with your own samples too, loading wavs into the drum computer or a sampler.
I'm just going from my experience so it's not absolute truth or anything, but of all the software I've tried, u can't beat reason for ease-of-use when ur starting out.