Not sure who would finance the rather impractical purchase of a rocky island off of City Island that is sometimes underwater at high tide, but there's one for sale if you're interested. I would assume that there is no electricity or plumbing, so this wouldn't be ideal for a residence, but you can't beat the views. I guess you'd also have to have marine transportation to get to a fro, but if you're buying an island you probably have a boat.
The unfortunately named Rat Island is on the market for $300,000. "'It's a nice, unique spot,' Red Brennen [the current owner] said. 'I cleaned it up in anticipation of selling it. So I'm just waiting on offers. Only serious ones, though. No tire-kickers.'" [NY Daily News]
To make a "serious offer," call (718) 928-6598.
"For Enough Cheese, Rat Island Is Yours; Family Wants 300G For Spot Near City Island" [Tanyanika Samuels, Daily News]
*photo courtesy of http://bratislav.files.wordpress.com/2008/08/p7026272.jpg and may or may not be rat island*