Bali is not all about the beach as say Phuket is.
It depends on what you are looking for, Nusa Dua is a white sand beach on the south coast but the area can be a bit sterile. Then there are beaches around Kuta & Sanur. I prefer Sanur, its a little more laid back and balinese. The east coast has darker volcanic sand beaches but can be lovely with the backdrop of huge volcanoes.