Copperbar

There a^([sic]) quite a lot of effects you can get with horz.retraces, eg a textmode copperbar (change color #0 with every scanline)

Although most cards still support screen-tweaking, you can just forget about copperbars (writing within horizontal retrace fuks up the screen BADLY) and other effex. Same goes for changing the font.

There was also the (really pretty famous) RSI Demomaker that let u make up your own intros/demos from a load of stock effects (bobs, starfields, copperbars, scrollers etc).. havent been able to find that tho...