The best show I've been to was one I actually booked, basically because I booked my two favorite bands. I doubt any of you would know them but the two headliners were Ed Gein and Engineer. Two great bands if you're into anything that Botch did. It was a fantastic show from seeing them play one after another to being able to share the bill with them (my band at the time opened). Attendance was great as the place was so full you could barely walk around. I made a profit on the show to boot.
As far as on a giant scale with world touring bands it would probably have to be the Pledge of Allegiance Tour back in 01 or 02. Slipknot, Rammstein, System of a Down, American Head Charge, and No One. While I don't listen to any of those bands anymore outside of Rammstein and Slipknot, it was a phenomenal. It was before System of a Down was all about politics and they played their whole set with a porn movie playing behind them. Rammstein had enough pyro to blow up a city and Slipknot was just plain awesome. I've been to Slipknot shows with people who don't like them and left saying "Man, that was a good show". They get a bad rap due to lots of their fans being total idiots but they bring the goods live. I'm really hoping Rammstein comes back here after their next album comes out.