If you haven't. - don't 
Mine are easy mongrels but ye gads we have...
Vets
Insurance
Food
Equipment (crates, bowls, beds etc)
Dog walker
Holiday cover
Training/behaviourist
Chiropractor 
But then.. Wait for it...
Dog suitable car
Lost earnings through dog ownership
The last ones are huge for us! Over the course of all our lifetimes we have/will pay thousands that we wouldn't pay if we didn't own dogs.
I met someone who had paid £5k to fly a rescue dog from the USA to the uk. Couldn't bear to be parted.
It's not for the faint hearted is it?