Not a documentary as such but TV series about fashion:
Blood, Sweat & T-Shirts!
It's about going from the high streets in London to the sweat shops in India, to see how & where the clothes are being made. The thing is though, there are 6 people each time who have to literally go & work in the sweat shops... It is amazing, the amount of energy that goes into a single garment...and how it is handled by many different individuals all putting their energies into them before they hit our stores to be sold for a squillion more than the people who made them are being paid! Made me want to get into sewing my own clothes!