Dogs
Shadow - She came to us with her name, and we just kept it.
Micki - He has Mickey Mouse shaped spots on his back and side
Mini - She's Micki's sister, so we had to name her Mini.
Kyra - Thought it was cute and it fit her
Jack - Absolutely hated the name, I wanted to name him Bonzai but my family was opposed to it...but Jack fits.

Cats
Motchka - I had just gotten home from a month long Europe trip with a group of Slovakians. I learned a TON of Slovak words and Cat in slovak is pronounced Motchka (but actually spelt Moćha) and I thought it was cute...and different.
Batman - I just gave her a random name, really wasn't planning on keeping her at all.
Jasper - My mom named him Paris until she found out her new baby girl was a boy. Jasper means hidden treasure, pun intended

Guinea pigs
Henry - I wanted a big masculine name for him
Elvis - I named her when I thought she was a he. I put a bunch of names in a hat and drew one.

Tokay Gecko
Geico - She came with her name.