In reply to BrianT:
The obvious choice would be the Ha Long Bay area - DWS, plus some bolted stuff at Butterfly Valley on Cat Ba island.
There are bits of climbing elsewhere, but not that much from what I know. Mostly just a few crags that have been developed by locals for top-roping. We explored the far south around Ha Tien (close to the Cambodian border) as we had seen some pics that suggested there may be DWS. Unfortunately the water was very shallow, and the rock had been mostly blasted apart for quarrying. A really interesting cultural experience though, and easy to cross over into the Kep area of Cambodia from Ha Tien.
Basically, Ha Long Bay is the short answer!