Amazon.com / 2012-2013
I left Match.com for Amazon.com after only a year because I was essentially poached. Amazon offered me a great deal to move out to Seattle (where I remain) and I couldn't refuse.
Although my time there was short it's safe to say that I had never worked harder or longer than I did working on the detail page team for Amazon.com. The struggle was real.
As the sole web-developer for the team responsible for providing the technology to rewrite the detail pages of amazon.com in Java (a big step up from the old Perl system) it fell to me to do first-pass implementation and prototyping for many of the several dozen amazon.com detail page variants. That means a fair amount of the code running the detail pages today is still mine :)
It was a surreal experience overall. The hours were insane, the projects enormous and the stories I can tell are sufficiently epic that I felt accomplished and justified in leaving for greener pastures after only a year. It was definitely worthwhile, but sadly unsustainable. Still, I look back fondly on my time with the leviathan of online retail, and I wouldn't trade it for anything.