There's a lot of debate around about what to do and what not to do with master bus. Personally i believe master bus has huge impact on final mix sound and I believe in 2014 anyone can use anything up to their personal preference. (DO NOT MISTAKEN MASTER BUS FOR MASTERING but that's for less experienced engineers or producers)
I always start my mix from setting up everything and I mix into the master bus chain. I wanna make sure I keep the balance of the mix the way I want, instead of mixing and then applying f.e. compression and changing the whole feel of the song.
I start from routing the signal to Dangerous Music D-Box. I use 4 Stereo groups for instruments, effects (instruments fx/ vocal fx) and vocals.
Next in the line is Chameleon Labs 7720 as my main bus compressor to do some light gain reduction, usually 1-2 dB at most
When I mix mixtape things and I don't wanna recall the settings from CL7720 I use Slate Digital VBC.
For 1st stage of saturation I use Sonnox Inflator. I use only touch of it, usually my settings are: effect 30%, curve stays at 0 and I don't play with input and output.
Another stage of saturation is Slate Digital VTM, quite different from Inflator, but I like to combine these 2. Depends on the mix I like to play with speed, tape type etc.
Kush Clariphonic is usually applied somewhere in the middle of mixing (not always needed) but sometimes I want to get that extra clarity and push the mix a bit more. A touch of Clariphonic creates magic.
The final tool in the chain (but used the least) is Izotope Ozone 4 harmonic exciter. I usually use it when I have to deal with poor quality instrumental most likely ripped of youtube. I always use it in M/S mode for better and more flexible tweaking.
This is my chain, obviously some of you guys might be surprised, some shocked, some might think I'm crazy and some might disagree, but as I said before it all comes down to personal preference. One day I'll elaborate on what and why is done, and what benefit the tools give to the mix.