pouët.net

i always liked iguana - despair. https://www.youtube.com/watch?v=MTeEwYz5GJ8&feature=youtu.be
i think the first part uses some feedback/screen buffer for the blur effect
and the part at 2:18 is a very good execution of an effect seen before on pcs and amigas in that time

pixtur, although ferner was 2008 and white one was 2010? ;)
speaking of inspiration: white one in turn was inspired by this video or one very similar to it: linky (analog video feedback from the 80s)

hmm, better capture https://www.youtube.com/watch?v=wi8bETwxexE
keito: your youtube capture of iguana-despair is broken man :D

I just remembered an old intro with good feedback. All I remember apart from that was it was 64k and it was one of the earliest demos built for windows (95 or 98 period?)

There's some feedbackish things in the beginning of Babylon that I've always been partial to even if they look slightly messy nowadays.

There is some nice feedback in Closer by CNCD (1995)

Here is some good collection of original experiments by Flexi: http://webglplayground.net/gallery that he is recently trying to port to Shadertoy (as noby provided a link).
but you probably have seen already if you interested in pattern generation using feedback.

pixtur: googling "Reaction Diffusion" should also take you to some useful resources, f.e. this.

This one is almost entirely made of feedback effects with evolving params: http://www.pouet.net/prod.php?which=52781

Like half of my stuff but especially in http://www.pouet.net/prod.php?which=53898

reaction diffusion looks pretty cool to explore

Trans Cheddar Express has a really nice feedback/particle thingy in the middle that starts around the 5m30s mark.

also this high quality prod has a medically correct model of photopsin depletion and regeneration in the human retina and its effect on color vision, which is a feedback effect.

let's not forget Difuze here =)

Best one: http://www.pouet.net/prod.php?which=7084

@Ara, @psenough: Yes! I spent quite a bit of time on the reaction diffusion-stuff yesterday. I'm pretty excited :-)

A lot of prods I didn't know so far. Amazing. Of course Difuze is pure magic.

For Potion, i ported a JS/ WebGL fluid effect from a close friend to C++/OpenGL. The source is not really a demo but nevertheless : here you go

Super cool!

Thinking of it, the smallest feedback "demo" might be Amoeba, a "core-free 2-neighbourhood" effect in 26 bytes (yep, i totally coined this term myself) ... considering the previous, you might want to contact Felix, the author of the turing fluids. He does WebGL based feedback stuff since ages and jumped for joy when shadertoy finally introduced buffers ^^

I looked at the earliest 64Ks for windows on pouet, found that intro I remembered pretty fast :)

Photon by Purple