Well, let's have a think about it for a second - couldn't be bothered searching for somebody else's answer (which there of course, must be here somewhere :p )
A mirror and a piece of glass are very similar, no?
While you can't see through a mirror, and it reflects pretty much 99%+ of the light that hits it, a bit of glass is see through and reflects no-where near that amount of light.
So, for starters, we could take an example from a material we used for a mirror, and turn the transparency value up to nearly full. Also, note that glass isn't usually black in shade, unless it's volcanic glass or, the 'glass' that's left after a nuke has gone off.
Sooo, we also need to change the colour. You've seen the edge of a window before, right? Well, unless it's high-purity glass (=expensive), it's more than likely that it will have a green hue to it.
So, why don't you try with a new blinn material. Set the colour to a green or a blue.
Next, you need to make sure you can see through it, so set the transparency up pretty high - almost to the end in fact.
Now stick that material on an object, and give it a go.
You'll nead quite a bit more work to make it look photorealistic, but the effect is there. It just needs more work and a good understanding of the hypershade, which comes with time.
As an example, the shader used to make a good-looking car-paint (with the reflections, and flecks of metal, and clear-coat and if it's pearl, plenty more) can easily have a dozen or more nodes in it.
It's just time to experiment or (wink, wink) do a google search for "246 shaders for maya" - you can download a shader for the job, but it's still not the same as working it out for yourself, and developing a stong understanding of how all the different values interact with one-another.
The results of searching for "246 shaders for maya" with google are well worth getting. Many, many, many hours work in that little gem.
oh yeah, here's a render of a super-quick and nasty glass shader.