I just got rid of a single-glazed aluminium framed window (and also some other stuff) by putting it up on DublinWaste.ie's Free Trade website - [broken link removed]
I didn't get any money for it, but I saved the money it would have cost me to dump it, and it's nice to know it's not just lying on a landfill somewhere but that somebody is putting it to good use. And as the person who took it collected it I was very happy.
You could put yours up on eBay if you're set on getting some money for them, but it might be a hassle esp if you don't already have a track record as a seller.
BTW, I found the best way to take a photograph of what's essentially a framed piece of glass is to close the curtains and take the picture from outside. (Whatever website you post it on, you'll really need a picture to attract any interest)
If you are posting them on DublinWaste.ie make sure you post them in the right section - for windows it should be "Homeware and Crafts", sub-category "Doors/Windows". My stuff was all taken up within 2 days.
Good luck