This one pretends to be the longest domain name in the world:
Is it the longest? Domain names in .com can count up to 63 characters, so it is impossible to have the longest name.
Those are live too:
abcdefghijklmnopqrstuvwxyzabcdefghijklmnopqrstuvwxyz abcdefghijk.com (and you can get a fancy e-mail address there)
llanfairpwllgwyngyllgogerychwyrndrobwllllantysiliogo gogoch.com (slightly smaller, but the longest single word (without hyphens) .com domain name in the world)
fautvraimentetreconpouravoiruneadresseinternet aussilongue.com (the translation could be: One has to be really stupid to have such a long address)
My favorite was:
verizonshouldspendmoretimefixingitsnetworkand lessmoneyonlawyers.com :~)
UPDATE [6/20] Other long names on Bleu Blanc Blog.
UPDATE [6/21] And now Germans pretend they coined the longest domain name! Still, it's only 63 characters long. It's WiemenschlichMenschensindzeigtihrUmgangmitder Muttersprachefrsch.de (which means Just how human humans are is shown by how they treat their mother tongue).