Hi Poi, one more recommendation for Tulamben and also for Aquamarine Diving. I've used them whenever I'm there, they are very good but not the cheapest so it depends on what you are looking for. I would also highly recommend Secret Bay (it is near the Menjangen area). Tulamben can get pretty crowded, but it is still a very good experience. 3 weeks in Bali sounds great, excellent diving plus a lot of non diving activities! I know that Demon84 recommends the Gilis, I haven't been there myself, most people seem to prefer Bali.