My personal greatest demo of all time:
Biohazard 4. This game was:
1. My first Japanese import game
2. My first INTERNET PURCHASE (begged my dad to let me use his credit card)
I also purchased a Gamecube Action Replay in order to play import discs. That's a lot of work for a demo, huh?
Well, it was fucking worth it. It consisted of arguably the best part of one of the greatest games of all time (the intro/village sequence of Resident Evil 4). I must have played through that demo at least 50 times. If you collected 30,000 ptas (not easy), you unlocked an Uzi, which was AWESOME. I used action replay codes to turn off the timer, and I'd just run around the empty village looking at stuff.
So, so good.