There can be only one: Microsoft Tech-Ed.
Specifically, 2005 was a very good year: SQL Server & Visual Studio both came out at the same time.
I’ve also attended Code Camps (free, community-led, Microsoft-sponsored weekend events). These are cool, too. Buy only Tech-Ed brings together the big names down under. I get to go every three years (our team rotates the privilege). My last one was 2008. I’m hoping that the current economic conditions don’t prevent me from attending this year.
I love the ability to audit various streams of IT: Database, Web, Windows, Visual Studio, Security. And if I get bored with all that, I can just mosey into a lab and teach myself the latest patterns. Outstanding.