Gotta get this if you're going to try mastering stuff free.

[Fimbulin]

http://www.voxengo.com/product/span/

It's free- and it's awesome! You will still have to manually EQ, compress, and limit everything, but this shows you exactly what you are doing to your mix.

[Applejinx]

...but I already swear by it, especially 'density mode' O_O

[Stars In Autumn]

I'll definitely try this out on my remix entry. Looks awesome.