I've got a couple. My sign-in name at work is a shortening of my last name -- it comes from the fact that mid-80s UNIX only allowed eight character user ids, and I've used it whenever I had a choice of what id to use.

My name here is because I like Aardvarks. Back in college I decided to become obsessed with Aardvarks (or the word Aardvark) instead of sex. I hate having numbers in an ID, so if there is already an Aardvark I become something else Aardvarkian. At Deviant Art I'm Asymptotic-Aardvark. (Which means that I'm approaching but not reaching the state of being an Aardvark.)

The other ID I use a lot is "Janitor of Lunacy", which is the title of a song by Nico.