Well to do TV shows based on DC character you to think low powered cause of the FX. Look at how Smallville is, thy very little of the powers cause of the FX budget.
My suggestions would be:
The Question - one of my favorite characters
The Blackhawks - WW2 heroes in suped-up fighters
Green Arrow - I see done more with him
Martian Manhunter - An alien detective show
Sandman - the pup hero version could be interesting
since the supernatural is big now how about these:
Hellblazer - Done right with the blonde hair and british and since does mostly palor trick in comics it could be done for tv.
The Phantom Stranger, Mr. E, Deadman (powers of a ghost and possession), Doctor Occult and few more vertigo titles.