Rails.
"Holy shit, I can build the same stuff that I used to build, except it will take me less time than PHP and be more stable, clean, and maintainable than Java. How the hell did I live without has_many :through before???"
"Holy shit, I can build the same stuff that I used to build, except it will take me less time than PHP and be more stable, clean, and maintainable than Java. How the hell did I live without has_many :through before???"
Others: * Google Sketchup (This was only last week --> It's so simple!) * VM Snapshots * ITunes library/playlist structure (Don't laugh... The unified library showing every song was a revelation after mucking around with winamp playlists and folders.. Also - I remember winamp really sucking on the mac at the time) * HTML - "You mean I can publish stuff on the Internet and people can read it from across the world?" (I was about 11 at the time ('95))
And yes, I'm referring more to the overall feeling... It was one of those things, when I first saw it I couldn't believe it was true. I thought, "if it looks too good to be true, it probably isn't true". So I didn't try it for about 8 months. When I did finally try Rails, it turned out I was wrong. It was true, and it is on a different level than what I was used to before (Java and PHP mostly).
Quite the shock.