I imagine you're not a US citizen? Don't believe it was ever available here though I know it was a HUGE hit in Europe and elsewhere.
I'm torn between 3 of them:
Dream
Moto Droid
Nexus 1
Voted Droid since it was my first Android. First one on Verizon (again a big deal for US folks), brought Moto back from the dead, had a huge developer community, first with 2.0. All and all, I think it put Android on the map where it wasn't so much beforehand.
The N1 was the first Nexus device, and while for all intents and purposes was a failure for sales, was an important step forward for the Nexus line.
