Ozzfest 2006 - First and best concert ever. I got to see System of A Down play before they split up. Unfortunately I saw Dragonforce play, but it was still an amazing experience to see a lot of great bands play in one day.
Buzz Bakesale 2007 - A Florida music fest held once a year around winter time. Got to see quite a bit of different alternative bands play, including Three Days Grace.
Megadeth (2007) - Phenomenal performance live... It was their tour to support their United Abominations album which was new at the time. They sure gave us a good show and I will always remember it.
Metallica (2009) - I finally got to see the band that got me into metal in the first place. Was and will always be one of my favorite metal bands ever. So much energy while performing and it was one of the best shows ever.
Megadeth (2009) - Yes, I got to see one of my favorite bands play again. They were that good the first time. In this performance, they were just as awesome as they were back in 2007. As an added bonus, I got to see Machine Head open for them and they are also another thrash metal band that I consider good.
Trivium (2009) - A pretty new-ish metalcore/thrash metal band that has amazing talent and by the time they reached their early/mid 20's, they already made 4 studio albums and are currently working on a 5th album. This band is highly influenced by my favorite, older metal bands such as Metallica, Machine Head, Slayer, etc... They were amazing live and I saw them play in their hometown, Orlando FL. Hoping to see them again to promote their new album sometime next year.
I am planning on going to Mayhem Fest this August since a few good metal bands will be playing this year. I will come back and post about it if I felt that it was an amazing performance.