Long story short: sugar.
I don't remember where I found out about this, and I'm sure a fair amount of you know about it already, but for the last few months whenever I've cooked a meat dish where you want a quick transition between a good char on the outside and some pink on the inside (basically beef and lamb), I've been adding sugar to my spice mix and it noticeably improves the crust. Basically, it enhances caramelization (AKA the Maillard reaction), which is just another way of saying "breaking down sugar", by increasing the amount of sugar that's being broken down.
The science behind it, by my understanding; is that sugar is made of 6 carbon atoms, 12 hydrogen atoms, and 6 oxygen atoms (that's the basic formula for the simplest forms of sugar, and table sugar is a combination of a couple of different kinds, which complicates things a bit but it doesn't change the general numbers enough to matter much to the topic at hand). Once it's heated to a sufficient temperature (350 degrees Fahrenheit? I think that's it but I'm too lazy to re-check at the moment), the bonds break down and the atoms can rearrange themselves so that the 6 oxygen atoms re-bond with the 12 hydrogens, making water (H2O) which then boils off and leaves only the carbon behind.
It's entirely possible I have some of the details wrong, and if so let me know, but the general principle is definitely sound and it's made a noticeable difference in the stuff I've made where it's applicable, so I figured I'd pass it along.