The Suicide Squad (or Task Force X) were a group of DC comics villains who were gathered together by Amanda Waller for some of her more "difficult" missions..in other words these guys were like the dirty dozen of the DC universe, it was never a sure thing to return from a mission in one piece.
Justin Marks, whose super-prison screenplay “Supermax” utilized wrongly accused DC icon Green Arrow as well as its own giant cast of established DC supervillainy, is scripting “Suicide Squad” for Warner Bros.
No definitive word on which supervillians will be utilized for the movie, but those serving on the squad in the comics include Batman enemies Penguin, Poison Ivy and Deadshot, Flash enemies Captain Boomerang and Captain Cold, Green Arrow enemy Count Vertigo, Atom enemy Chronos, Justice League enemy Doctor Light, and Superman enemy Parasite.
I think this could be a pretty cool movie..provided Warner Bros. give the filmmakers the go ahead to use DCs most prolific superbastards of course!

Heres a full list of the characters that have appeared in the team, some regulars some guest appearances:
Amanda "The Wall" Waller
Atom II
Atom III
Batman I
Big Barda
Black Adam
Black Orchid
Blockbuster I
Bolt
Bronze Tiger
Captain Boomerang I
Captain Cold
Captain Rick Flag Jr.
Catalyst
Chronos I
Copperhead
Deadshot
Dr. Light III
Duchess
Enchantress
Enforcer II
Firehawk
Javelin
Jewelee
Karma
Katana
Killer Frost II
King Shark II
Knockout
Lady Liberty
Maser (Air Wave II)
Major Victory
Manhunter III
Mindboggler
Mr. 104
Multiplex
Nemesis I
Nightshade
Oracle
Outlaw
Parasite
Penguin
Plastique
Poison Ivy
Psi
Punch
Ravan
Shade the Changing Man I
Shrike
Sidearm
Silent Majority
Silver Swan I
Sledge
Slipknot
Speedy
Sportsmaster II
Stalnoivolk
Thinker I
Thinker II
Vixen
Weasel
(The) Writer