There are plenty that come to my mind when I think of retro demo’s - but something I did years ago which I rarely find myself doing now (probably because I have a lot more desposable income) was LUST over demos. Tekken 2’s demo on Demo One with the PS1. Sega Rally Demo which featured on a Saturn Mag (someone brought this up in the SR thread) are two very notable demos, however for me; I have some real odd faves:

Quarentine on the PC - a one disk PCZONE cover demo, played it over and over and couldnt work out how they got so much content into the demo.
C&C 1 Demo: PS1 (or saturn, not 100%). One level, over and over and over…

I’m sure more will come to mind! What about you guys?