A human-reviewed and curated list that's comprehensive, searchable (everything on the list is indexed, nothing off the list is indexed,) and ad-free. Businesses who aren't on the directory, but would like to be, pay an application fee. The huge secondary industry that sprung up around DMOZ indicates that this business model would work.

There'd be more to it than that, but that's the basic idea.

I'd love to find enough people who would like to work on such a thing.