tarted out with satinaya@cats which is a pc misspelling of my SCA name which is Sata Naya. I didn't really want to explain to people why "satan" was in my login, so I just altered the spelling a bit.
Tiger became my nick when I got an account on the brand new circus.com. I had an affinity to felines and tiger@circus sounded so very cool. Little did I know just how appropriate it would be. Over the years, I've found a great many personality traits that are rather tigerish. Some have advantages, some have disadvantages, some have both. Territorial, fiercely protective, and unwilling to share my food are some of the main ones. Oh yeah, and bitey, though that one is mostly Craig's fault :]
Tiger also has the additional advantage of not inspiring the "Ooo, that person must be female." reaction that way too many early internet users had. I don't like getting fan mail from strangers and my cats account name inspired way to much of it.
On icb, I am snow_tiger because there was already a registered tiger. The snow part came about because Craig had just recently taught me to ski and that was cool.