Playing around with minified C I wrote a renderer for the Mandelbrot set in 228 bytes, using some abuse of boolean logic.

#include<stdio.h>
#define F float
void main(){int i
=4095,j;while(i--
>=0){F p=0,q=0,a=
-(F)(i%64-14)/30,
b=(F)(i/64-32)/30
;j=99;while(j-->0
&&p*p+q*q<9){F s=
p*p-q*q,t=2*p*q;p
=a+s,q=b+t;}j=~i&
63?')'-j/10:'\n';
putchar(j);}}

And here’s the expanded version so you can see how it works:

#include <stdio.h>

void main()
{
    int i = 4095, j;
    while(i-- >= 0)
    {
        if(i % 64 > 0) /* give us newlines every 64 chars */
        {
            float p = 0, /* re(z) */
                  q = 0, /* im(z) */
                  a = -(float)(i % 64 - 14) / 30, /* re(c) */
                  b = (float)(i / 64 - 32) / 30;  /* im(c) */

            j = 99; /* 99 iterations computed */
            while(j-- > 0 && /* iterate */
                  p * p + q * q < 9) /* check for divergence */
            {
                float s = p * p - q * q, t = 2 * p * q; /* z^2 */
                p = a + s; /* z = z^2 + c */
                q = b + t; /* ........... */
            }
            putchar(')' - j / 10); /* print different character
                                      depending on iteration count */
        }
        else
        {
            putchar('\n');
        }
    }
}

Of course, there would be little point telling you if I didn’t show you the output, too. Here it is, looking slightly out of proportion due to the non-square characters in my terminal emulator:

The Mandelbrot set rendered as ASCII art in a terminal emulator.
The different 'levels' of iterations required for the sequence to diverge are shown using different characters.

Not only was this a fun little challenge to write, but it also taught me what the Mandelbrot set actually is - prior to this point, my knowledge of the fractal was limited to what it looked like.