I remember reading (probably here somewhere) that Batman and the Green Arrow appear on the show.
Do any other DC heroes make an appearance?
Green Arrow yes, Batman no. The show features a lot of other DC characters, however. They are limited in that they are often prevented from using characters Warner Bros has other ideas for - like Batman and Wonder Woman. As far as heroes go you've got:
- Green Arrow (Oliver Queen - played by Justin Hartley, a regular on the show)
- Aquaman (Arthur Curry)
- Impulse (Bart Allen)
- Cyborg (Victor Stone)
- Black Canary (Dinah Lance)
- Zatanna
- The Legion of Superheroes (specifically Cosmic Boy, Saturn Girl and Lightning Lad)
- Supergirl (Kara Zor-El/Kara Kent)
- Martian Manhunter (J'onn J'onzz aka John Jones)
Clark is an on/off member of what he jokingly calls the "Junior Lifeguard Association" (JLA, geddit ?), a group funded by Queen.
Green Arrow, Aquaman, Cyborg and Impulse made individual appearances before showing up together in "Justice". Black Canary and Chloe Sullivan joined later. Chloe is given the codename "Watchtower" as she is the eyes and ears of the League. Clark is jokingly codenamed "Boy Scout" as he often clashes with Oliver over their respective methods.
The show has also featured numerous DC villains in addition to Lex Luthor such as Doomsday, Zod, Faora, The Toyman, Mister Mxyzptlk, Morgan Edge and Intergang, Brainiac (played by Buffy's James Marsters) and others.
As
nx1701g alludes, there was a cheeky reference to a "Theymiscrian Princess" visiting Metropolis.