Thanks for all the great feedback. I've added a Canon 20-35 f/3.5-f/4.5 to the list of things I'm considering. It's cheaper, maybe as little as $150, but slower and not as wide. Any thoughts? Speed isn't a primary consideration and 20 is wide enough on a FF camera. My primary concern is image quality both for landscapes and with flash for nightclub work.
I just want something wider and lighter than the 24-70, but I feel I am selling myself short a bit by picking up such a small wideness gain, but it is a very inexpensive lens. For some reason, i kind of cringe at buying a 3rd party lens. Silly of me, most likely.