Check out the mastering forum They have lots of threads like this. In fact, I think there is a thread going right now regarding someone who wanted to buy mastering software... and I think the general concensus comes down to the fact that you really shouldn't need to do much in so-called "mastering" software, since you have access to the mix itself.
I.E. if the bass drum is too heavy in a certain frequency range, fix it in its own track, vs. applying degenerative EQ to the overall stereo master. There's just no point in doing the latter.
But, I don't really master my own stuff, since I haven't really gotten finished with a lot of my own work, so don't take my word for it - roll down there and check it out!