Because I write a lot, I always have a big mental archive of names (I should probably write it down sometime). Some of my sim names come from names of original characters I've created spanning years back. I also like borrowing names from musicians and actors who I think have interesting names or who I like; I often splice them together and see what happens. In fact, some of my names even come from songs themselves (lots of Smashing Pumpkins songs have female names in the title so I decided to roll with that as a theme on one occasion as an example). Other times I can visualise the sims I want to make and then the names just happen that way. When I have writers block, I just hit up Behind The Name.