The first program I purchased was FruityLoops. It was a great program, easy to use and created some nice beats... but I didn't have the patience to push through all the options to figure out how to tweak sounds to give them that natural sound that I was looking for. Keep in mind this was a few years ago and they may have made changes to fix this issue.
The next beat making software that I purchased was Reason. This program was really cool, made great sounds, and it was extremely user friendly. I used this progam for about a year before I made the change to a keyboard. It didn't take very much time to figure out, and within a day I made my first beat... it wasn't great, but it was a beat.
Recently, I've run across another program that I think is definitely worthy of some attention. DubTurbo. Like how I gave it a sentence just for itself? The program is great. As I mentioned with Fruityloops, a major issue was making the sounds have a natural feel, but DubTurbo offers great sounds and the only tweaking you need to do is for effects... if you don't want natural, you can give it a robotic, synth feel. Which is solid, because you really shouldn't have to tweak a sound to make it sound natural.
Another great aspect of this beat making software, besides its price (it is affordable, especially when you look at the price tag on other programs- which don't measure up to this software), is they offer a video tutorial to get you up and running pretty quickly. If you are a visual learner, then all you have to do is follow the video, and about 10 minutes later you can be Noddin' your head to your own beat. A final thing I like about their program is their sampling ability, they offer a nice chunky variety of samples to play with and the program allows you to import sounds if you are looking for a specific sound.
Check out their beat software at: DubTurbo.
These are Samples of Beats Made with DubTurbo