Wow, I wish these guys were putting on a concert near me. I found these guys this weekend as I was poking around YouTube to show my son the original gameplay of the 1990s Prince of Persia.
Here's some of my favorites.
Super Mario Bros. Medly:
Metal Gear Solid 2 / 3 Theme:
Final Fantasy VII: One Winged Angel:
You can go check them out here if you want more info: