I'm lazy when it comes to mastering, which is probably why my masters aren't as good as people who select each individual processing FX and adjust each one.  I have Izotope's Ozone 7.  I just add it to my master bus, click on one of my favorite presets, do a little tweaking in each of the modules and call it done.   I end up with a final mix that's punchier, has more stereo separation, and better EQ'd.  The punchiness is just boosting the loudness, but I'm careful not to add too much.

If you can afford Ozone, don't like spending a lot of time mastering but have a basic understanding of mastering, this is one of the quickest and painless ways to go.  They have dozens of presets for different types of music and individual instruments.  You can just go with what the preset offers, or tweak a little bit to get it just how you like it.
The only drawback with Ozone is that it's a memory hog, so I always add it after I'm done writing and mixing the song.  If you try to play with Ozone, even with a fast computer, you get glitches and dropouts.  But as I said, the results are often quite fantastic.

A project I'm working on at the moment uses 96K/32-bit,  20 individual tracks and 4 or 5 group busses. I've been light on the effects so far because I want to save any final effects like overall reverb until the end. Even though I have an older 6-core AMD setup it seems to be coping. Original done in an older Cubase 2.2 project bounced out from the C9 demo.
 
The tracks have been divided, bounced and trimmed as well. So that should save on the resources. Anyway I decided to enable to performance meters and noted all 6 cores were in use all under the 20% however as I lost so much work in the past through crashes and file corruption I still work this failsafe method.
 
I have one folder for working projects and another for mixdowns & masters. This keep things tidy and organised for me at least.
 
Plug-in wise it's a mixture of Cakewalk, VSL Suite, Focusrite, Universal Audio to name a few which I am using to bring all the sound together. Because the track was old and had some reverb added already, I had to narrow the stereo width and using a De-Verb plug in to remove some ambience.
 
Ozone is a fantastic all in one package, it's very flexible and Izotope themself publish mastering tips.
 
I really want to upgrade to remove all the bottlenecks in my setup. 

interpolated
Yeah it is, I like to be able to balance everything on it's own. Probably a throw back to working on large projects with under powered computers. I did readdress the question saying just a stereo mix without any final compression and limiting would be also work.
 
People work in different ways.
 

I've done some Stem mastering  as well.
It has its uses for sure. I find mastering stems has different sound characteristics compared to mastering a stereo file. For example if you put delay or reverb on your guitar stem file, they tend to be enhanced 3X fold in the master because the limiting, compression and multiband EQ are hearing the delay/reverb  lot cleaner than if it was some what drowned in with a stereo file. Theoretically it shouldn't because the stems are being summed to the master bus, however, I found this is not the case, the repeats become clarified and pronounced.