1. Early Ruby on Rails -- Now that MVC/ORM packges are the norm, it's hard to describe how revolutionary the original '15 minute blog' video was. It really felt like a quantum leap for CRUD apps.
2. Uber/Lyft - It has literally remolded the city I live in, by making large areas that are transit-inconvenient more attractive to live in.
3. Linode -- Access to a cheap server that you could spin up/down in a minute with root access was really great, in an era where a server that wasn't just a junk shared host often required months of commitment and started at 100 bucks a month.
4. Google Maps -- Just head and shoulders above mapquest.