
Kuta
Kuta is one of the most popular sites; you can now find basically any surfing equipment there. As the sun approaches the horizon, you can see lines of Balinese approaching the beach, controlling their surf-boards with the same gracefulness as their traditional dances, mastering the waves and penetrating the tubes. Even in Kuta Beach and the area around it alone there are places for difficult surfs. It's best to talk to the locals so you won't get into trouble.
Uluwatu
On the southern tip of Bali, Uluwatu is also high on a surfer's destination list. The road to the beach is pretty well-hidden, off the road to the temple of Uluwatu (which in itself is an amazing three-court temple on top of a few hundred feet cliff). You can't reach it by car - rent a motorcycle or walk for about two miles to get there. The site is very popular among serious surfers.
Nusa Dua.