When rendering 3D glass, it is nice to have something for it to reflect. If there is little of the environment to reflect (because it is not built in 3D, or in 2D Photoshop, you must supply the reflection) a seamless reflection map is needed. This map is intended for a use at a very low reflection... just a hint of the map, yet enough for detail to start to show. It has activity, yet little vagueness that makes it not distracting. Enjoy.
This seamless texture was created by Patrick Hoesly, and is released under the Creative Commons Attribution license. Download more free textures by scrolling through this blog.