Most of the forums I have seen are really lame pirate-oriented sites. I am interested in joining in a discussion with programmers about building iOS software that breaks the rules, but not illegal stuff.
A number of developers are on IRC on Saurik's IRC network:
Also note you will probably get better answers to jailbreak questions at Jailbreak QA. No questionable questions are allowed there. And you will not get a good response if you have questionable repositories in your Cydia configuration. Just how things are.
Most forums I have found regarding iOS hacking usually involve piracy at some level (whether that be getting apps or in-app purchases for free).