Chhunin exams arc.
Introduction of many awesome characters including my favorite; multiple interesting fights, dat tension in forest of death, and of course Lee vs Gaara fight; they all make it epic.
I'm agreeing with ya'! The Invasion of Pein arc was amazing. One of the better arcs the manga has had. Though, The Sasuke Retrieval Arc and Orochimaru's invasion of Konoha were also very well done and great arcs too.
