I used to play board games and Age of Empires in Zone.com (now MSN Games) and I onced changed my email and had to create a new profile. All my usual usernames were taken, so the site recommended some from a random list of adjective-noun pairs. One stood out among the list: “LimitedMage”. It’s unique (Google it and you only get results related to me) and I like to think of it as cool and bad-ass.
I kept using my other regular usernames (julip and julipena) for a few years, but eventually limitedmage stuck. I still use my other names for some sites (eg. http://digg.com/users/julip), but most of my online profiles now use what I consider to be my online identity.