I've had a running list of my book titles and character names online and in my computer for years. I started it with the characters when I realised I had too many characters with the same first name. Mind you, not all characters end up with the names I gave them. Editors have a habit of changing names, or asking me to change them. I do it, but I don't like to, because since my too-many-Jennies discovery, I've taken considerable care in naming my characters.
Now and then, I rename a character on my own recognisance, usually because my first choice doesn't seem to suit or because it's too close to someone else's name. Recent changes were Cari to Nanette and Colin to Henry--both done when I realised there were too many characters with the initial C.
Along with this, I have an ambition to have book titles for every letter. I almost do--there's even X and the Pony and Zoo-Thology, but I don't have any others for X or Z and none at all for Q. I have precious few characters with Q-names or U/X/V/Z names either. I popped a Valentine in I Promise last year, and I have a couple of Quinns and a Quentin. I've just finished a book with a character named Xanthe. It's not that there aren't names beginning with these initials, but many of them are culturally incorrect for the books I write, or they're difficult to pronounce, and from the wrong era or just plain ugly. I keep stubbing my toe on Queenie. I may use that one day, but it has to be the right character... wish me luck!