batsbrew
 
RAIN,
you might want to investigate Sony Acid.
 
i used to have it,
and created some killer drum grooves very quickly with it.
 

Actually, I'm quite familiar with it, from my PC days. ;)
 
But admittedly, I've never been big on (audio) loops. So far, the most satisfying solution has been to use MIDI grooves and customize them. 
 
I think Apple are onto something with their Drummer plug-in - instead of simply browsing through endless lists of grooves, once you've picked your "drummer" and a basic groove, you "tell" your drummer how you want him to play via the GUI. More/less hat, softer/louder, more/less fills, hold back on the cymbals, etc...
 

 
 
There's something in it that's very close to the way I used to work with the drummer in our band.
 
Obviously, there's a lot of room for improvement - the minute you start to think about customizing pattern, the tools at your disposal lack the precision. But I can see how it could evolve into something very powerful.
 
That being said, at this point, I've used it more for the actual drums sound - because you can use Drumkit Designer without the Drummer plug-in/track - which fit better in my music than the rest of my libraries. These drum libraries account for 20GB of content, so it's not like it's a poor man's alternative to similar 3rd party libraries in terms of sound quality/diversity.
 
 

My understanding of Mastering is that its primary goal is to make multiple songs sound and feel like they're on the same album/CD? You can have two different mixes which are fine in their own right, but may not gel together as they should if they were part of a compilation. 
 
H-

Making multiple tracks gel nicely is certainly one of the goals of mastering.  (In level and tone or EQ qualities)  And one way to do it is to choose a track out of all the album tracks you have and master that first.  You pick this one track that best represents the total sound of the album.  It might be one of the biggest sounding tracks as well.  What you can do is to master this track first and called this the album reference track.  Even while you are mastering this track you can still switch to some nice commercial references that are right in the ball park.  That never hurts.
 
Now you master all the other album tracks in any order.  What you do though is have this reference album mastered track sitting inside every track mastering session.  And on a track muted most of the time.  You get cracking and master the next album track the way you want to and when it is close to complete you compare it to the album reference track and see how your newly mastered track stands up.
 
Often all that is needed is just a little change to the EQ mainly to match things by a lot.  It makes a world of difference, having your first mastered ref track around.
 
The trick is to choose carefully the first ref mastered track.
 
The other trick is to send these special ref tracks out to a different set of outputs on your interface and organise to switch incoming stereo signals using 2 trK monitor input selection or do it on a mixer you can solo real fast. It is better when you can switch around and compare tracks as fast as you can. You have less time to forget how something sounded.