V.P.I. is a good one.

All insurance requires that you pay up front, then apply for reimbursement.

Instead of insurance, many owners advocate getting a high-limit credit card with a good interest rate and ONLY using it for emergency vet bills -- keep it in a drawer or cabinet at home where you won't see it often and where you won't be tempted to use it for other items. If you have the self control to do this without using it for other things, it's a good option, doesn't cost you money out-of-pocket right away, and allows you to pay with installments. This way, you aren't paying yearly or monthly insurance premiums that you may not even use, especially if money is tight.

When you select your pet insurance, read carefully and see what is covered. Some policies cover certain illnesses or injuries only after you've had the policy a set amount of time. Also, decide what the 'high risk' area of your dog is and select your insurance accordingly. If your breed has a high incidence of cancer, carry a cancer rider with the policy. A very active dog may need extra coverage to cover costly surgeries to injuries common to active dogs such as ACL tears and joint surgery. A lazy dog that doesn't ever leave the fenced yard or house shouldn't need to carry as high of coverage for activity-related problems as a herding dog that works stock every day.

Also, I've found it's not worth paying extra to have 'routine treatments' like vaccines, worm medication and flea/tick/heartworm prevention covered. In most cases, it is far less costly to pay for these routine things out-of-pocket and carry insurance only for larger items like surgery, diagnostics, emergency care, etc.