Have you tried flights.google.com?
* Awful, text list of flights. I want a way to visualize the options, to wisely choose from many options.
* Subset of the airlines. Google still has Delta at least, which has disappeared from Hipmunk and some others. But no Southwest.
Also I really like the flexible dates view [1]
Shame about Southwest for sure, but I think that's more on Southwest than anyone else (do they list their flights on any aggregator? I remember hearing somewhere that's part of their shtick is that they don't)