I have LOTS of those moments.
InFamous: When I got the lightning storm. And then got to use it while on a sub-station that gave me unlimited charge. And then I killed 10 goons in one storm. I looked at the sea of toasted enemies and went "...I am unstoppable. First sons...Run for your lives. I am coming for you."
Halo 3: Me and a friend ended up alone against a team of 3 higher level guys. We. Won. It was a tough match and we only won by about 3-4 points, but we won. Not to mention we had our own music playing the background, and all we got were kickass songs that time.
Sanctum (FPS tower defense): I was on Medium difficulty on the Bridge. I realized I had 2 waves left to go, and my core was untouched. I was in the middle of a wave when it hit me that unless I made a VERY big mistake, I was gonna clear the level flawlessly. With a quiet whoop, I hurled myself at the enemy and made it happen.
When programming: I was doing an assignment and something was just not working. Then It clicked. And I got it working. And I did the most epic fistpump ever.
Borderlands: I play a Siren, my pal plays a sniper. We got cornered by (no joke), 2 badass corrosive scags, a badass electric skag, and a bunch of normal skags and psychos in a cave corridor. ...I was crippled (dying) due to being attacked from behind by the psychos, and I saw that the badass corrosive skag that I had been attacking was nearly dead, and the psychos were finishing it off. I then said "NO. That's MY kill! Hands off!" and killed it, getting a second wind (revived). Two phasewalks and a grenade later, they all lay dead around me. Apparently, my friend survived a similar situation.
Mass Effect: All those times I swept through enemies like a...like a...great biotic wind!
Timeshift: ...When I realized just how invincible the ability to bend time was in conjunction with the shotgun or fire pistol. I cleaned rooms out in seconds.
Mirror's edge: Whenever I made it through a level without dying. I felt like the wind incarnate.
That's all I got right now.
EDIT: OOH! And EVERY. DAMN. KILL. in shadow of the collosus. Specifically the last boss. As I was approaching it, and it kept shooting at me, and every time it missed, I made the hero whistle as if to say "I'm still here. I'm still alive. I'm still coming for you!". I taunted that thing with my whistle each time I had the opportunity. I wanted it to know that I would end it like I did all the other collossi.