The energy sword, Halo 3.
Back in Halo 2 I loved the sword but if it ever came to a point where I was versing people with it I would die over and over. Around the time of Halo 3 however they improved it with the 'counter' thing and BAM! Suddenly sangheli360 (My Xbox Live alias) was hacking his way through legions of spartans as a proud elite.
I love my energy sword so much I'd kiss it... if it wasn't for the fact that it would slice open my cheeks.