Free stuff* is always nice, right? Zopfli is really nice, now I just have to try the bread as hell.
$ time zopflipng -m democracy-for-sale.png test.png Optimizing democracy-for-sale.png Input size: 673908 (658K) Result size: 411196 (401K). Percentage of original: 61.017% Result is smaller real 0m23,125s user 0m18,019s sys 0m0,052s
* comes at a slight computational cost.