i've been too so many gigs already I really don't know what the best one was.
Here are a few:
In Flames at Wacken Open air 2007. They were headlining and the show was amazing. It was huge with fireworks and everything that a good show needs.
To be honest all the concerts I've seen of In Flames are so good. (And i've seen them already 5 times)
Eum This year I saw Metallica. Was also very good.
36 Crazyfists, Iron maiden, As I lay dying, Killswitch, The Black Dalhia Murder, Dilllinger Escape plan,... They're all so f** good live!! And i've forgotten lots