Homemade sterographs
Here's a linK (sorry it's not direct) with instructions on how to build different stereoscopes:
http://www.funsci.com/fun3_en/stscp/stscp.htm#6
This site also has some good images to practice with. Years ago I made one of these slide things, works pretty good, but I used velcro to hold it together. Now that I've good digital photos, I don't use it that much anymore. A good mirror scope is way pricey. I recomend the pocket steroscopes, here are some at the reliable Ben Meadows Company (a field research outfit company):
http://www.benmeadows.com/store/dept.asp?dept_id=524
The student scope is only 8 dollars.