Demoscenes literally pack a punch. In 64kB, they display an amazing array of graphics combined with awesome music. The first of such demoscenes to come my way was a video called "Heaven 7" in 2001. I did not know back then that it is a demoscene; but it did capture my imagination.
Later, I found that it was an award winning entry at the "Mekka & Symposium" demoparty 2000. The developers (Picard group) extracted last ounce of the hardware's power through efficient coding and ingenuous tricks. A description of the same will be worth reading for those inclined towards programming. Also to be noted is that each participating group acknowledges others towards the end of the demo.
The "Mekka & Symposium" evolved into a new avatar, "Breakpoint" in 2003. It got huge sponsorships from ATI in subsequent years (before ATI was acquired by AMD) and became the largest demoscene party to be held annually. The awards are given in many categories because of the diversity of platforms on which demoscenes are being made make it difficult to compare their technical efficiency on a common benchmark. I particularly liked the winning entry for 64k intro in PC category at Breakpoint 2005 - Binary Flow.