Sonnox Oxford Inflator by fearoftigers
I stumbled across the Inflator whilst on the lookout for a more transparant clipper.
The clipper I had been using often added some undesirable elements and I wanted something cleaner and less noticeable.
The Inflator instantly blew me away, first with it's ease of use and second with its almost effortless ability to raise the perceived loudness of any audio signal.
The controls are very simple indeed with two sliders, one for 'effect level' and one 'curve'.
There is also a band split button which I've found smoothes out the processing on certain signals.
There's certainly no rocket science to using this plugin, just see how much you can crank the signal without it distorting. If you're processing individual channels then this is probably all the way.
On the master bus, I've found this plugin works really well between the EQ and the limiter to give it that really loud flavour.
In summary, if you're looking for loudness then this is the plugin for you.