Regarding Daredevil's Rogues Gallery, its bigger then one would think, here is a couple of lists of DD's rogues gallery:
http://www.rapsheet.co.uk/rapsheetmain/Daredevil.asp
http://en.wikipedia.org/wiki/List_of_Daredevil_enemies
Plus Green Arrow has a even smaller rogues gallery then DD and they just pulled out the most obscure villains around and give them episodes, like Dodger and China White, characters who I never heard of before they appeared on screen or they use C-list Batman villains like Firefly.
DD's rogues gallery is a mixed bag, you got great villains like Bullseye, Kingpin, Typhoid Mary, the Hand, etc and you got a lot of lame villains like Leap-Frog, Stilt-Man and Matador and you have some villains in the middle, good to okay villains, who may get a good story once and while.
I actually like Purple Man and I don't think he is been a goofball since appeared in the Alias comics, which presented him as a psychotic rapist and serial killer who abuses his mind control power to the furthest extremist. He is actually pretty creepy in that comic, whether he works in a DD TV series is a bit debatable, but he is far less goofy then Stilt-Man. I also think, while he is somewhat over the top, so are Bullseye (a guy who runs around NYC killing people with paper clips) or the Hand (an evil demon worshiping cult that can bring back the dead).
I think Gladiator (Melvin Potter) is a must, because he is interesting, yet underrated character. He started out as a villain and became a member of DD's supporting. He is a somewhat more realistic take on a mentally ill character, his madness has a particular method (psychotic delusions of being an actual Roman gladiator) and once he is cured of his mental illness through drugs and therapy, he is horrified at what he did while in a psychotic state. It also interesting to have a villain actually go straight and went to be a better person.
Mr. Fear is kinda of a tough one, one of the hand he is one of DD's more personal villains, having a grudge against Matt Murdock before knowing he was DD, which is the opposite of what most villains react towards to Matt and he is one of the major villains in Brubaker's run, but on the other hand, he may be seen as a Scarecrow rip off, even though I am pretty sure he used the fear gas gimmick before Scarecrow did, though that may not matter to the general public. He's not a truly shameless rip off, like Jester is, where Stan Lee ripped off the Joker and put him in a DD comic.
You can also do something something the Marvel movies have done, take the basics of a character and change everything else about them. For example, Ann Nocenti introduced the Wildboys in her run, a pair of street punks who caused trouble, you can expand that to an entire street gang named the Wildboys, a group that works at the bottom of the criminal food chain, being the ones who actually sell the drugs on the street for example.
I kinda like Bushwacker and Mr. Hyde, but they may be tricky to do on TV budget, though I do like the story where Matt has to defend Mr. Hyde for one particular crime he didn't commit.
There are also tons of stories where DD does just fights normal criminals, his origin story involves him going after a mid level gangster named the Fixer who murdered his dad, there was an interesting story from the Miller era where Punisher was targeting a mid level drug lord who Matt represented in court, which was an interesting contrast on those characters viewed the justice system and the story where DD fought 100 Yakuza members was really good.
Really DD is the kind character, where you can tell great stories of him fighting super villains or just regular criminals, you could tell some interesting stories with some of DD's B-list villains, but the only one who I think is a must have is Gladiator.