Joseph Jaffe is one of my favourite authors since he often focus on interactivity between brands and customers and on pull-based advertising. On Monday on iMediaConnection he wrote Inviting Interaction which I think is a very good collection of useful examples to look at. Online marketing is evolving and it's moving towards consolidation by stressing the key aspect of Internet communication in comparison to other media: interactivity.
Of course this doesn't sound new to most of you but, again, I believe it's good to go through best practices to keep it in mind.