Letters
I was looking for an example of off-beat things to do with sub-domains for my piece on using sub-domains for digital gardens and decided to make one for each letter of the alphabet.
These are those sites:
a, b, c, d, e, f, g, h, i, j, k, l, m, n, o, p, q, r, s, t, u, v, w, x, y, z