I use Spectrafoo from Metric Halo. Very slick. You can set up a bank of meters with whatever you want to see. Level meters, phase, freqency a couple ways, and others.
I like to be able to see where the thing I'm not liking is faster than fishing around for it with EQ. I also like the way you get a feel for the overall EQ shape of a mix shows up. Helps me know if my ears are skewed too far off.
But, yeah, in the end, ears should make the final decision.
Oh, but clients love how it looks...