There are a few in WPB. If you go to Singer island and park at the Hilton(which you can do as long as you purchase lunch or drink etc..). Also you can park at Ocean Reef park which is a tiny park just north of the Hilton. Once you get behind either place, if you are there during lower tides, you will see a big rock sticking out of the water. There is great snorkeling all around that and in the general area...and its free. Another place is on Peanut Island right in the intracoastal near the inlet. You can get to Peanut Island by taking a water taxi from the Sailfish marina on Singer Island(cost 5 dollars) over to Peanut island.

www.floridaadventuring.com/peanut-island.html

http://www.sailfishmarina.com/water_taxi.html

Also check out this website as there are several companies that can also assist with setting up a snorkeling tour:

http://www.westpalmbeach.com/activities.html

have fun.