As far as beaches go, some of the nicest are in the Sarasota area. Siesta Key especially. There's also excellent snorkeling in a couple of spots. But all the diving is further offshore and a lot of it centers around wrecks. The gulf in that area is pretty sandy and flat for a long way out. Here's some details - if this link doesn't work it's from the Florida Underwater Sports website. http://032393e.netsolhost.com/WordP...1/Florida-Underwater-Sports-Dive-SIte-Map.jpg You'll notice the two words in most of the site details are shallow and sandy - it is.
Most diving around here is offshore, but not all. There are several good shore dives in the area depending on your level of experience, from shark tooth diving (beginner) to the phosphate docks in Boca Grande (advanced). There are artificial reefs and even an old (and admittedly barely there) wreck off the beach in Sarasota.