Two-Face is an old school gangster, folks. Loud suits, tommy guns, "hits" and "heists", thugs in coat and tie. He's the Dick Traciest of Batman's rather Traciesque Rogues' Gallery (and if you don't believe that, go look up Haf-n-Haf who first appeared in 1931).
A gangster needs a gang! And Two-Face needs one more than most. While Two-Face is certainly always disturbing (in some ways the most disturbing of the Bat-enemies), he's not always as threatening as we need him to be. Brilliant and sturdy though Two-Face is, Batman's basically fighting a burn victim with a law degree. While others sport freeze-guns, mind-controlling headwear, and exploding whoopie cushions, Two-Face carries ... a gun. Let's give the man some back-up, shall we?
The Joker's themes (clowns, humor, cards) are more style than substance; he's not really known for stealing objects or planning capers around his themes. The Golden Age Penguin used go pretty heavy on the themes (birds and umbrellas), but lightened up dramatically after the Crisis.
But Two-Face, as we all know, is really big on "theme"; always has been. He would definitely have lieutenants who shared one of his themes (the number two, justice, chance/fate, gambling, the coin). So I'm picturing:
Double Dare and The Body Doubles (already foes of Nightwing and classic examples of Free-Range Sidekicks)
The Trigger Twins (foes of Robin)
The Penny Plunderer (*sniff*, I love you, Joe, no matter what they say)
Hazard and her brother, The Gambler,
Jinx and Amos Fortune (if you play Heroclix, you know the value of "Probability Control")
The Bad Samaritan (which would keep me from donating him to Marvel)
Larry the Judge (Tec #72!)
a moll named Penny or Silver (gotta have a moll)
and for some comedic costumed chaos, Dollar Bill (surely some of you remember Dollar Bill!)