http://www.complex.com/pop-culture/2014/05/10-dc-villains-who-should-appear-on-arrow/

From immortal terrorists to ninja assassins, find out who made the cut.

http://www.cinemablend.com/television/-7-Classic-Comic-Villains-Arrow-Needs-Use-68732.html

With the exception of the corrupt businessmen and no-name criminals that Oliver Queen faced in the first episodes of Season 1, Arrow has done a tremendous job of featuring a variety of DC villains. Not only have they included most of Green Arrow's rogues gallery from the comics like Merlyn, Clock King and Count Vertigo, but they've also grabbed villains from other corners of the DC universe to antagonize Starling City's archer, from Teen Titans villains Deathstroke and Brother Blood to the government sponsored Suicide Squad. This season the main antagonist is Ra's al Ghul, someone who has primarily fought Batman. Whether a villain belongs to a specific hero doesn't mater as long as that villain fits into Arrow's narrative. So don't think for one moment that Arrow will be running out of villains for Oliver and Team Arrow to face.

Arrow hasn't even begun to scratch the surface of bad guys to throw into the mix. So we've put together a list of comic villains that we feel would thrive in the dark world of Arrow. Whether they are deadly martial artists of favor brains over brawn, they all have something in common: they would give the Starling City vigilante a run for his money.