I have submitted an island generator to the unity asset store for $20.
Creates an island terrain from a simple template image.
Additional bumps, hills can be placed using perlin noise over the non-beach areas of the island.
Includes mass placing of trees and details. Lots of options for controlling how they are placed. They are not placed on mountain tops or beaches unless you want them to be.
Lots of options for customizing how the island will be generated. Almost all the options include tool tips.
Includes bumpmapping as standard. Just delete bumpmap shader if you dont want it.
Uses standard unity terrain. (Other terrain editor assets can be used to add further mods)
more info
Website
Video
Webplayer
The terrain shader was originally built by Chris Morris of Six Times Nothing (http://www.sixtimesnothing.com), its Free to use and modify.
Terrain shader was improved upon by Larsbertrum1
http://forum.unity3d.com/threads/116509-Improved-Terrain-Texture-Tiling