Depends on what you want. For more power try doing some squats, dead lifts, bench press, and pull ups. Mix it up with some kettelbells. Do whatever cardio you enjoy. Of course swimming would be most beneficial to surfing.
Most of all stay dedicated, do whatever exercise you enjoy 4-5 days a week with intensity. Your off days are important, your body needs time to recoup.
Check out the Vasa trainer. It simulates the motion of paddling, and builds all the right muscle groups. It also has other workout options for other muscle groups, but for building paddling strength, I've never worked out on a piece of equipment like this when I can't get in the water.