Wow - that's a tough one pakman. I've been spending all my hard earned cash over the last few years to fly from Singapore to North and Central America to video a few sharks as the bloody Chinese seem to have eaten anything larger than a dogfish over here.
OK *rant off*
Layang Layang can be good in the season for hammerheads, but not as reliable as Cocos or Galapagos.
One usually sees a few reef sharks in the currents off the Maldives, but you'll see many more mantas. Lot's of white tip reef sharks at night too, but that's probably old hat for you.
The threshers in the Philippines at Malapashqua have become less reliable, although they turn up at the strangest places - we had one swim through us on a dive at Crystal Bay in Bali a while back.
Whale sharks are very dependable at Donsol south of Legaspi in the Philippines, but that is snorkeling only and the viz sucks. We saw around 45 over three days but for only about 2 minutes each! Better to go to Belize, although they are semi reliable in places around the Andamans.
I'm hoping that Raja Ampat has a few sharks left, but we never saw many other than epaulettes a year or so back, and after seeing shawnh and jbonehoss video and photos it seems the finners are there too!
Probably the best places to see specifically sharks over this side of the globe IMHO would be off the Barrier Reef and the Coral Sea, eg like Osprey Reef, but I don't know whether you'd consider that Asia.....
There are probably tons of secret Asian shark places I don't know about - eg I believe Komodo has a shark or two. But the biggest concentration of sharks I've seen here is at couple of shops behind Boat Quay in Singapore, but that's another rant .....