How best to present long equations in two-column papers? How best to present long equations in two-column papers? 

I've tried splitting them in two or more lines along operators, but that still looks a bit weird to me, especially when parentheses have to be carried along across the lines. Also, I've considered stretching them across both columns, but that seems only an acceptable solution if the equation is of outstanding importance, e.g. the final result and not some middle section of a proof.
When I have had occasion to deal with obnoxiously large equations, I find that there are four strategies that do well for me.  In order of readability, they are:


Shrink the font: if you are allowed (any many venues do allow this), you can usually shrink the font on an equation a few points without affecting readability.
Map separable terms of the equation to new variables, which can be given their own independent definition lines.  This can really help readability in a complex equation as well.


--- The line of desperation ---


Break the equation across two lines: this works up to about 1.6 lines worth of smaller-font equation.  When combined with adjusting font size, you can often adjust where the break occurs to make it look reasonable.
Move the equations to a full-width figure, where you can play all of the same games.