That grey slab of a console launched in the US September 9th, 1995 and September 29th in Europe. Home gaming was never the same.
The Sony Computer Entertainment Japan webpage has a timeline of all things PlayStation, though because it's technically 15 only in Japan it's of course all in Japanese.
Still it'll be 15 years old come September 2010 for us here in the West, and then we can have our own spiffing timelined website of Sony product nostalgia - yeah! Did you own a PlayStation back in those retro nineties? It changed everything it did.