mastering is a massive artform. and i'm one of those ppl that would rather master myself and not leave to someone who doesnt understand where i'm coming from. but each to their own.. if you want to get into it, you need to read this as a start point: bob katz 'the art and science of mastering audio'. you have to understand eq, compression and limiting in it's entirely (and multiband too) and i mean ENTIRETY... i would suggest reading at least an hour a day on the subject for a year (and i'm not joking!!!)..... t-racks is good cause it's an all-round suite that help you understand how it all works, but it's certain not the best... plus things like how dither or bitrate etc affects what you're doing if you're working in the analog/digital world, as well as tricks involving stereo field that can make your bottom end sound punchier and top end sound wider..

for mastering soundforge is pretty industry standard on a pc.. peak is cool on a mac but i would definitely rather do it on soundforge... oh and use the plugin chainer if you're on soundforge rather than just applying each effect individually...

ok hope this helps as a start...

ps the point about reference tracks is soooooo right imho. i mean, if you understand the principles of mastering, every decision you make when mastering is made based upon the tune you're mastering and what you know is right for the music you're trying to make. and that's thousands of decisions that go to make the whole. but you use a ref and bam, you've made 6000000 decisions based upon someone else's track. which is bullshit of course :)