Well, there's obviously this username, first of all...I've used that in only a few places so far, though (all pokemon-related things). It's a more recent name, at least in regards to using it for myself.
Then there's my main internet name, Nepryne, which is what I use to sign up for other kinds of places (like art sites, non-pokemon oekakis, things like that).
Then there's a few others names I've used, either when "Nepryne" was already taken (by me, I should hope), or before I even started using that name (there's at least one place out there that that still applies to...).