some cool presentations !?

what are some top conferences or presentation that you think every hacker should have watched or at least be familiar with,

ps; just wanting to get a deeper understanding of the culture and maybe see the bigger picture o the mentality ,

I've been watching defcons and stuff , and i came across some really interesting presentations by some really cool people, i mean i'm really sure i haven't watched all of them, so if you happen to know some cool links, help a brother out.