Sometimes I spend weeks trying to find the right name. For Echo in the Pushing the Limits series, her name was originally Sarah. I knew that wasn't her name, but I couldn't come up with the right name so Sarah served as a place holder. I finally found Echo about halfway through writing the book.
For Hendrix (Drix) in Say You'll Remember Me, since his father was a musician and Drix played the drums, I spent a lot of time going through rock musician names and listening to their music to find the right name.