Dreamcast - I won a lot of money off my friends with that system!

For me its a race between 3. My old Sinclair Spectrum 128k, my Commodore Amiga 1200 (both computers i guess...not consoles) and my PS3. I still marvel that a game like Damocles on the Amiga could be made at that time, be of such huge scope and all fit on a single load 3.5 inch floppy disk. An entire solar system to fly, drive and walk around in first person. Amazing.

Nintendo 64. It could be partly sentimental since it was my entire childhood, but no other console has had that many awesome games attached to it.

The Atari 7800 was the perfect storm for me. I never had a 2600, and stores were still clearing out all of the 2600 games when the 7800 came out, so I was able to load up on brand new games for a couple of bucks each. The cartridges are long gone, but I think the console is still somewhere in my parents' attic.