Well, for very small intros (4k/8k) distance fields are still hard to beat due to their compactness. A couple of examples not based on distfields, off the top of my head:

http://www.pouet.net/prod.php?which=62027 (No idea what this is, but it's great)

http://www.pouet.net/prod.php?which=62974 (reverse fluid simulation)

http://www.pouet.net/prod.php?which=59613 (particles)

For 64k intros and size unlimited demos the possibilities are too many to list. Procedural mesh generation is a classic approach which has found great modern use recently:

http://www.pouet.net/prod.php?which=61204 (if you follow 1 link in this comment make it this one)

Awesome, thanks!

What kind of mathemagical trickery is that reverse fluid simulation?!

Seven held a short seminar about it, it's the first one in this video:

http://www.youtube.com/watch?v=DQ8eB_FORLo