Lesleen M is a great wreck to explore. The pinnacles near Soufriere are also great, but pretty challening current sometimes. Great outfitters are Scuba Steve http://www.scubastevesdiving.com/dive-sites and the dive base at Anse Chastanet.
For more ideas on what to do when you visit St. Lucia, go to www.travelintense.com/eco-travel-destinations/saint-lucia. about 4 years ago