Balinese beaches are overcrowded. Just go to Bali for cultural traditions and temples.
For the beaches, just flight 20 minutes East to Lombok. The surf spots are incredible, you can swim, ride horses www.chevalkutalombok.canalblog.com or dive (Gilli's). The area is totally unspoiled by mass tourism.
If you decided to visit Bali for its culture, living traditions, rice fields and night life, you will choose Lombok for the most spectacular white sand beaches of Indonesia (see picture). Only 20 minutes flight East, several flights a day.
If you don't like too much to visit a country in the middle of waves of tourists, in Bali avoid the South area (Kuta, Semyniak, Legian, Benoa, Sanur) wich are packed-up. Stay in Ubud and go around North and East regions (kingdoms). The main temples are in this area, the beautiful ricefields also. Loose your way in little roads between Klungkung and Iseh or Banjar, or Munduk, here is the true, genuine Bali of postcards. If you prefer nightlife go South !
In Ubud, stay in Legal Sari www.legalsari-ubud.com or Waka di Ume, and if you want to experiment the most luxurious and refined hotel in the world, try the Begawan Giri and ask for Wanakasa Master www.begawan-giri.com. In Ubud, have a good meal at Naughty Nury's, it's the best Spare Ribs I ever ate and the Margharita is hummmm.
For the beaches I would say most of Balinese beaches are disapointed (and some dangerous), the best one are in Lombok, South : Kuta. The spot is unspoiled and the beaches and bays are spectacular. Here you can surf, swim, snorkel, go fishing or ridnig good horses (www.horseridingkuta.canalblog.com) . It's wild and great. No nightlife and quiet location.
My choice there is www.villa-lombok.com (beautiful view, private villa) or its guest rooms on the hill also www.flickr.com/photos/eudaimon .
To reach Lombok 
direcly from other countries through Singapore or Jakarta :
Singapore-Mataram : 3 flights a week with Silkair (Monday, Thursday, Saturday)
Jakarta-Mataram : 4 flights a day with Garuda, Merpati, Lion Air, Batavia
