Reply to composing tool for backing beats

So, in my area 'real' drummers are very very (very) sparse, and most suck. Also, my band needed some cool sound effects.

Since the bassist is interested in DJing eventually (as am I) we figured we might as well dive in to learning Beat composition software to create our drum tracks.

The main thing I am looking for (right now) is the fast and easy ability to create drum and effects tracks that sound good.

I work on a Mac, he on a PC. So, hopefully there is an excellent option available for both, but if not, we'll adapt.

Suggestions?