The only legit one I've seen is a Medical Transcriptionist or Medical Billing Agent.
And even then, it usually involves working IN the office for some time, getting experience, then doing it from home.
SABRE tried having reservations agents work from home a few years back, and it really was a joke. The person basically still worked the hours they normally do, PLUS they had to completely control the background noise in the home (no kids, no pets), and make sure they were available the right hours. You still had to ask for a bathroom break, but now, instead of raising your hand, you had to call someone.
I would say that, with the tight economy, these jobs are few and far between and work ONLY when you already have an established relationship with your customer.
If you don't already have a customer who will pay you to work from home, then DON'T BOTHER.
These newspaper/email/spam ads for work from home are an opportunity to TRAIN you to work from home. But they aren't going to bring you any customers or even leads.
Glen Austin