Isabela sites includes:  Isla Tortuga, La Viuda, 4 Hermanos and Roca Union - accessible by land.  Live-aboards dive Cabo Marshall, Roca Redonda and Punta Vicente Roca

On Isabela are 4 dive sites accessible by land, 3 accessible by liveaboard and others that no one goes to anymore after the Park abruptly put a halt to cruises that were permitting diving and were not strictly live-aboards...in the infamous year (of our Lord & Master & Commander [part of which was filmed in the Galapagos, btw] - PNG) 2007.  We do have access to our 'secret' site that some proclaim to have been as good as Darwin and Wolf even though it's not a shark site per se.  It's a pricey charter though, so only inquire if you're a group.

Though it's not a dive site, Los Tuneles is a snorkeling site where we always take our divers because it is such a magical place.  See a description and photo gallery of Los Tuneles on our blog.