Dark Imagery... HAAHHAAAAA!! awesome.
Umm.. a good pair of ears?
If you don't have that you won't be able to master.
There's no one piece of "mastering kit" that professional engineers use I'm afraid. It's all about listening to the track in a good environment that you know well, and giving it whatever it needs. Reverb, EQ, Compression, requesting less compression (my personal favourite!!), all that kind of stuff but ONLY when applicable.
If you want to master your own recordings, I strongly suggest getting a professional to listen to it, especially if the recordings are any good. The far cheaper and quicker option would be to post the mix in the MP3 clinic, and get some feedback from the wonderful people on this forum! Maybe then you'll be able to have a bash at 'mastering' it, but again I'd get someone experienced in a proper listening environment to listen even after that.
If you want to set yourself up as a mastering engineer.... then I suggest you go and get some experience first before you buy anything. Not only will you learn what pro mastering engineers use in terms of outboard or plugins or whatever, but you'll find out if you've got the ears to do it.