I usually use the name Incursus. I spotted it whilst flicking through a Latin dictionary once and I was immediately taken with the sound of the word. Whilst I then read that it meant 'attack', 'assault', or 'onslaught' didn't matter to me by then. I was already in love with the sound of the word.
However, when creating a username for here I didn't think that something that meant attack or assault seemed appropriate - at least it didn't sit well in my head for somewhere where people are being so emotionally open - so I decided to go with another Latinised name and went with Argent, from the latin argentum meaning silver.
Again, no particular reason, I just liked the sound of the word. :-)