Envelope stuffing sounds like a great way to work from home. Just pay x amount of dollars, receive the literature, and the orders start rolling in, right? Wrong! What the ads for this opportunity don't tell you is that you have to get out and beat the bushes, contacting a list of places who might or might not be interested in having envelopes stuffed. By the way, many of the places who used to use this service now have a machine doing it.
Another thing to stay away from is the HUD refunds thing. Frankly, this one gets very close to being a scam. It works much the same way as the envelope stuffing thing. You pay your money, get the literature; and contact the list of names of companies that use this service. Why would a company that did this be interested in using amateurs to do this? The resources available on the internet can find people very quickly and efficiently.
Of course, there are the very real, very crooked scams such as the Nigerian letters, the lottery ticket scams, and many other schemes to separate you and your money. I will post more here as scams are discovered.