Al,
Regarding the banners, maybe you can have the best of both worlds. Have it open to all, and the ones that you know are reputable, you can label them "endorsed." A poll can be set up for those who have dealt with a particular sponsor, and give a positive rating, and set a number for positive ratings for an "endorsed" label. An alternative would be to give a subjective "opinion" on a site that it is "endorsed" by you, similar to how you are allowing sponsors now. The subjective opinion, as long as it is stated as such, should provide the site with legal protection. The poll would probably provide more legal protection.
I personally agree with ShinShin's suggestion to do away with screen names. It takes awhile to figure out who everyone is, and for the new people, it would help identifying who people are refering to when they alternatively refer to screen names and real names. I would think the real names would especially help those who are selling Discus. It took me a while to figure out which screen name was associated with the different sites selling Discus, and I still am unsure about some of them.
I do not know if it is possible to set it up, but there may be a way to have people keep their screen names, but when they post, a "signature" automatically lists their real name.
As far as the chat room, I think it is a good idea, especially for those times when someone is having a problem.
Just my thoughts.
Jim