How do you pick names for your Sims?

In past saves I have had a theme going. In one legacy, the surname of the founder when she married was Crystal. So all their 5 children had gemstone related names. When the males married this theme continued. When the females married they took on a new surname. For example one of the second gen girls married a man called David Danger. With the surname being Danger the first girl was named Lillith (after the demon) and actually inherited black hair and her sister was called Ivy (as in Poison Ivy) and she actually inherited red hair which was really cool. So I tend to have themes like that going.

In my current save my legacy sim is yet to marry and I need to think of a surname with a theme of the sim I want her to marry. It's kinda fun to have a theme.