Some things are inevitable at Ultra: Slamming main-stage sets from artists like Afrojack, Kaskade and David Guetta. The occasional pop star drop-by (e.g., Madonna, Will.i.am). Lots and lots of neon. But every year, there are moments of higher consequence: Sets that test if new artists are worth the hype, demonstrate the fervor of an upstart's fan base, broadcast the arrival of a new sound or trend, or give an established name a chance to renew himself. Below, seven such must-see sets over Ultra's two weekends. Don't miss them.