Dreadlords was the name given to men and women who could channel and sided with the Shadow in the Trolloc Wars (Robert Jordan Question of the Week, Week 12). Many would, of course, have liked to call themselves "Chosen" (like the Forsaken), but they were afraid to do so because once the thirteen trapped Chosen became free from the seals they might disapprove. Some Dreadlords had positions equivalent to the Forsaken in the War of the Shadow. They ran the Shadow's side during the Trolloc Wars, but they hadn't received the mark that would have given them the command over Shadowspawn. Even so, they worked together with Myrddraal as Commanders for the Shadow's armies. Many of the lesser of the original so called "Forsaken" were as weak in the One Power as most of the Dreadlords. There were in fact a huge number of Forsaken during the War of the Shadow, and all channelers that forsook the Light, from the strongest to the weakest, were called "Forsaken" during that time. Some of whom were every bit as high-ranking as the thirteen remembered after the Breaking.
So, who are the Dreadlords in the upcoming Tarmon Gai'don? We believe that Taim is with the Shadow and that he has at least a hundred followers (KoD, Epilogue), all of whom are probably Darkfriends. He has apparently used the One Power enough to learn as much as have (and without going mad from the taint), uses Old Tongue words, sent Asha'man to kill Rand, won't have his own faction to be bonded by Aes Sedai and his sigil (a gauntleted fist clasping lightning) is another sign of him having sided with the Shadow. He is almost as strong as Rand (LoC, Ch. 3), but he apparently didn't know how to make Gateways - though he knew the talent was called "Travel". He is well organized and he seem to have leadership skills. That does not correspond well with someone being "more than half mad", so that seem to point towards him not being Moridin.
Then we have the Black Ajah. They have certainly had time on their hands to recruit, among the Sisters, new Black Ajah members. We know that Black Sisters can indeed have Warders that are not darkfriends and Black Sisters can also bond recruited Darkfriends. Even so, one can possibly suspect that Red Sisters are over-represented among the Black and that Green Sisters are under-represented. At least among the Sisters that were recruited to the Shadow before they were Raised to the shawl.
Then we have Darkfriends among the sul'dam, the Aiel (especially the male ones) and among the Windfinders. It should perhaps be noted that a circle of thirteen can turn a channeler to the Shadow, so any male Aiel channeler that seek death in the north can be turned. Some people have also argued for the Ayyad being Dreadlords. It wouldn't seem far fetched that some of them would be Darkfriends, but probably not all of them (?). Male channelers in all nations and of all cultures have had an extremely strong motivation, during the last three thousand years or so, to pledge their oaths to the Dark One.