These assets has been obtained from : http://www.fantasticmaps.com/free-stuff/
All of these resources are provided free for personal use. There are many more maps available on my RPGNow and Paizo stores. If you would like to be notified when a new free map is posted, follow me on G+, facebook or twitter.
This set contains images that can be put together to create an infinite variety of dungeons: 14 textures, 10 markers, a full set of wall sections and 180 objects to flesh out any lair. All textures and images are sized to 100px per 5′ square. The tiles can be put together in an image editing program or in a virtual tabletop. The tiles are licensed for use under the Creative Commons license CC-BY-NC-SA.
These tiles and images were created by Jonathan Roberts for release with the stable version of maptool 1.3. They are licensed for re-use and distribution under the Creative Commons
share-alike, non-commercial, attribution license: http://creativecommons.org/licenses/by-nc-sa/3.0/