This year, the FOSS4G (Free and Open Source Software for Geospatial) conference is in Portland, OR in September. They are expecting upwards of 1,000 attendees.
They are looking for folks to present case studies. This is a great opportunity to show off your Cesium apps. See the Call for Presentations (due April 15) for full details.
Also, if you are attending and want to meet up to talk about Cesium, let me know.