I was starting a new campaign with two new players (and three old) and one of the new players was still working on character creation during the first adventure. We didn't want to wait, we wanted to get going, so mostly he tagged along (more roleplaying than combat then anyway) and whenever I had to refer to him, since he didn't have a name, I started calling him Amorphous-Blob - since he hadn't quite taken on defintion yet.
Later, that was shortened to A-Bob, and the next session, he hadn't thought of anything else and the name sort of stuck. It helped that he was a Psion who made blobs of goo when he manifested.
My favorite name was for an ordinary, 1st Edition fighter from way back when I was in elementary school in 1982. He was a fighter who just liked to throw flasks of oil. His only name:
The Mad Flame.