As goofy as the Bumbling Dad persona is, it is actually quite clever how he used Raven's friends to try to convince her daughter to be a Demon Spawn. It just goes to show why Trigon is considered the source of all evil. Fortunately Raven isn't stupid.
Beast Boy tricking everyone in the end. Taking out the context of them all dying and becoming ghosts, it's pretty awesome to trick the pranksters by going along with their prank only to then turn it on themselves.
The Titans have an incredible battle using a Humongous Mecha against Gizmo's giant robot army.
Not to mention Robin beating Gizmo with just a the left leg, with his upgrades to match.
Starfire turns out to be a surprisingly effective villain in "Starfire the Terrible". She blows up the moon and while her evil lair is made of cardboard, it has real lasers and a robot army that gives the Titans a hard time.
Robin and Cyborg accidentally combine their attacks to create an explosion so powerful, it can be seen from space.
Bonus points later for trying to combine other things, the first thing they try? Robin's cane and Cy's Jukebox, and the combination Works
Once Raven realizes how awesome her legs are, she gives them quite the workout. Just ask Jump City's villains.
Robin, Starfire, and Raven's trio in "Waffles".
Remember in "Super Robin" when Robin wore himself out beating Mammoth? Well, while infiltrating the Hive as Red X, he effortlessly beats the crap out of him!
Everyone's dream...well maybe except Beast Boy's dream in "Dreams".
Cyborg's voice and the Titans' dances in "Grandma Voice".
The Titans battling the Puppet Wizard during the season 1 finale to get their souls back.
Starfire's revenge on Blackfire during the end of "Mr.Butt".