I think starfield was the first effect I wrote as a demo coder in the 80s. Then a Copper wobbling picture I think (Like the Star frontier intro) - or copper bars, then a sin scroller. Nearly joined TRSA because one coder in our group was a genius (not me!) but deal fell through :-(
Oh man that would have been so cool! Sorry that it fell through..
I remember making infinite ASCII mazes by alternating forward and backward slashes in the late 80s early 90s. That would have been the grade school computer lab days for me and I didn't have the to do anything better so it was mazes or controlling the turtle in LOGO
I didn't own an Amiga but a friend of mine from school did. We had a blast playing Gobliiins!