I believe I have had a few:

Fallen_angel (original according to my profile but I am sure I used to have one prior to this where I had the same but "_666" on the end and I changed it because I was being aked if I was a satanist)
Lasuria (username I use in the online RPG I work as a developer for, before joining their staff I had quit for about a year from the beta testing. I was however contacted by players who had found me on here due to my username, against my wishes which prompted my change to Iceglow)
Iceglow (present)

I don't intend to change the username again, I kinda like the username Iceglow, it's pretty unique and always a cause for random usernotes about ice glowing.