Most of my advice regarding the procurement of 3-D glasses is aimed at those who only need one or two pairs. But some people need 50 pairs, or a hundred, or a thousand. Perhaps you are one of them.

I, for instance, needed a whole bunch of 3-D glasses. I wanted to give them away to my kids, to my friends, to my clients, and to my students at the college where I teach. So I shopped around for the best bulk deal on paper 3-D glasses.
I found it at Movie Vision, Inc. Their plain white 3D glasses are only 17¢ apiece. This price is substantially lower than other suppliers charge for plain white anaglyph glasses. I mean, it's less than half the price of the next best deal I could find! (Naturally, if you know of a better deal from some other company, please let me know in the comments.)
There is no minimum order; you could theoretically order just one pair, and pay 17¢ for it. But you won't, because there is a minimum shipping charge of $12.00, and $12.17 for a pair of paper glasses is not a bargain. This source only makes sense for people who need at least 50 pairs.
For example, if you buy 50 pairs at 17¢, that's $8.50, plus $12 shipping, for a total of $20.50. So your glasses will cost 41¢ apiece, including the shipping, and that's not bad. But if you buy 100 pairs at 17¢ plus $12 shipping, they're only 29¢ apiece. If you buy 1,000, they're about 18¢ apiece. So big orders save more.
And the shipping was quick. I placed my order online at 8:42 a.m., and just 24 minutes later, at 9:06, I got an email saying my order had been shipped! With a tracking number and everything. The package arrived two days later.
I should mention that I have no relationship at all with this company, I am not being paid to promote them, and I have no dealings with them other than having placed this order I'm blogging about. If anyone knows of a better deal on bulk 3D glasses from any other supplier, just let me know by commenting on this post, and I'll look into it.
UPDATE AUGUST 12, 2008: For at least the past five days, it has been impossible to place an order with MovieVision. Their website is up, but their shopping cart functions are all disabled. Nobody answers the phone, or returns my calls. Emails get no reply.
I also sent an email to their shopping-cart host, Website Forge, LLC, asking about the issue. My reply from them said, "This page has been restricted by the site administrator." That means it is not some technical glitch, but a decision by MovieVision to pull down their shopping cart.
I am not happy to see such a good source of 3-D glasses disappear, and I hope they come back soon. For now, if you need 3D glasses, I recommend buying from Rainbow Symphony, whose bulk prices are higher than MovieVision's, but a little lower than American Paper Optics.