SpaceUp: any of the regional ones. The previous SpaceUpDC was fruitful for me.
AAS (American Astronomical Society) twice-yearly meetings. I will be at the Jan 2014 one, in D.C.
AIAA (American Institute of Aeronautics and Astronautics) has focused topical conferences, plus an annual on Jan 2013 that might be worth attending. I haven't been, but a colleague recommends them, and I'd love to hear from others who have attended AIAA events.
AGU (American Geophysical Union) has an annual meeting in San Francisco each December, but I haven't found it very pico-relevant.
Possible SpaceOps, the every-2-year conference series? Others? In some ways, general conferences are becoming a dying breed. People now communicate with colleagues worldwide over the Internet, and the drive to travel just to mingle is lessened. However, I've always felt the high information density of being in a small, themed event with a core cadre (under 100) of people actually working on a topic is very fruitful.
Until next week (or next conference)
building Project Calliope here and also blogging weekly on general science