While searching for “Mysterious Islands” I have come upon these instances of Mysterious Islands. Here is a short list of those resources.
Ships of the Mysterious Islands is a Role Playing Game, and although the RPG has very little in common with the Whizkids game of the same name this RPG could add some interesting concepts and give a player some ideas on how to expand the Ships of the Mysterious Islands game.
The Top 10 Mysterious Islands in Fiction site offers ten examples of Mysterious Islands that have been mentioned in popular culture.
The Mysterious Island by Jules Verne is a must read for those Mysterious Island aficionados.
A tidal island is a piece of land that is connected to the mainland and can be reached by foot at low tide, however are either total submerged or are cut off from the main land at high tide.