I use Nationwide and the Whole Pet with Wellness Plan for Jax. He was diagnosed with IVDD last year and they paid 90% of his surgery costs and continue to pay 90% for any follow up visits and treatment costs.
I recently signed up with Healthy Paws. I have not filed any claims yet but I selected them because of reviews on several independent sites. They got high marks for customer service and unlike many plans do not have per incident, annual or lifetime limits on benefits. You can also select which deductible and co-pay you want. I wish I had more experience to tell you about. I'm hopeful they'll be good.