Blender 3D: Noob to Pro/Every Material Known to Man/Glass
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Material
Alpha: 0.1
Color: White (hex code: FFFFFF)
Shaders
Reflectivity: 0.2
Specularity: 1.5
Hardness: 511
Translucency: 1
Ambient: 0.5
Emit: 0
Mirror Trasp
Ray Mirror: enabled
Ray Mirror: 0.2
Ray Transparency: enabled
IOR (angular index of refraction): 1.37
- NOTE: I, a reader, suggest playing with the Fresnel for transparency.
Raytracing
Don't forget to enable raytracing on the render tab (Press F10 in the buttons window, then go to render tab within that window and click the button Ray which will enable the raytracing). Raytracing is enabled by default in Blender 2.37 and higher.
- This setting only applies on rendering while using Blender Internal, not suitable for others like Yafray.
Ickathu: Just in case anyone is stupid like me, this does not look transparent until you render. It is not transparent on the 3D view.
Here is an example of some glass that is less transparent and more reflective, almost a mirror. Just play with the "Alpha" setting until you get the effect you want.
Material
Alpha: .2
Diffuse Color: R .74, G .776, B .818
Speclular Color: R .676, G .732, B .798
Shaders
Diffuse Shader: Oren-Nayar
Reflection (Oren-Nayar): .959
Roughness (Oren-Nayar): .818
Specular Shader: Blinn
Specularity (Blinn): .731
Hardness(Blinn): 179
Refraction (Blinn): 10
Mirror Trasp
Ray Mirror: enabled
Ray Mirror: .56
Ztransp: enabled (this is very important, otherwise when you set your alpha value, only your backround color will show through, not the object behind the alphaed object)
All the rules for raytracing apply as written above.
Another glass setting. This one even has green edges by having different materials for them.
The Ztransp button should also be enabled, to allow the glass to show the material behind it.
Apply the green edges by using this material for the edges: 
