Personally? I like to avoid numbers in a username since they send a message that you lack professionalism. I have a twin brother, so I usually pick names that can have a similar or appropriate name (i.e. Castor and his would be Pollux, though we've never used those). Never underestimate the power of two cool words together (but do vet it against common sense, ChainsawMurderer is good if you're gonna put off a violent persona, PizzaCrusher is iffy, though it's really rather lighthearted so it could work well). Of course, the problem is that these aren't exactly rare names, so you may have to try a variation (ChainsawMurder or CrusherOfPizza) in order to get a similar name.