The three places that spring to mind are 1: Caves/ orange hill beach. North coast. mostly sand/ grass but with occasional coral heads. look for the dark patched from shore vantage then try to find'em on a compass bearing. Depth about 20'
2: Porpoise pens/ Clifton pier. On the Western tip. coral heads start from about 100 yds out and continue to the drop off wall at about 800 yds out. see the cesna airplane (stuart cove's "nari nari" site) Park in the securely guarded car park and walk down the path to the rock ramp. Depth 25 to 35'
3: Cabbage beach/ pirates cove on the north coast of PI. you'll have to access this beach from the eastern public accesses. either by RIU hotel or by the Atlantis laundry at the very east of the island (turn left just before Ocean Club Estates) unless you're lucky enuff to have an Atlantis band.Cabbage (eastern end) offers little except to the very east where the sandy beach ends in rocks that attract a whole lot more life, mostly smaller stuff. Pirates Cove offers the best stuff by far with any kind of gaurantee. the mouth of this absolutely idealic little cove has large Man made concrete blocks accross three quarters of it, starting from the eastern end. there's Loads of fish life in and about the structure. I've seen Large stingray, Nurse shark and puffer fish. Cow fish, sgt majors, rock hind and lots more. Sadly the amout of tourist boat traffic it means that you'd only safely be able to swim it by accessing it from the eastern rocks on a low tide when the boats/ water skiis/ nutters! stayed away from the shallow concrete. Even the use of an Blow up marker only means the real idiots drive over to see what it is! One more reason to carry that spear!
I've seen large stuff at 1: and 2: Eagle ray, Nurse shark, squid, lobster etc. Twice now an Octopuss at 2:!!
Good luck!
Dan
P.S. Do keep an eye out for the crazies on jet skiis!