My ShihTzu is Charlie just because it seemed to fit. I got him first and only named him a couple of days later. There were quite a few names being tossed around between my daughter and I before we both agreed to Charlie.
My Yorkie is "Littlest Mac" because our last name is MacDonald and he is the smallest in our family.
The new and upcoming Biewer puppy will be Teddy, I think... because who doesn't love a teddybear!?!?