Some fo you may know what the demoscene is (if not, learn about it ;) If you do, you've probably seen lots of amazing demos and cool 3D stuff (maybe even you've seen .kkrieger, a 96KB shoter with Doom 3-like quality ;)
But one thing I had read about but never actually watched until recently has been text mode demos. yup, MS-DOS (in "hi-res" ASCII mode) demos, hacking the color palette and doing every 3D effect you can imagine of, with ASCII characters.
Simply amazing. Fire, plasma, rotozoomer, spirals, donuts, tunnels, vectorial and 3D elements, multi-scrolls, scrolling texts, particles, "images"... Definetly worth looking at, you won't believe how they do it.
Here are some screenshots of 4 demos. In movement they look much more impressive: