I second this question. What are the best databases out there, that map IP addresses of office space, not web servers, to company names?

I see some products out there that purport to do this, but they aren't saying where they're getting their data. I'm really curious how they are creating such a database.

LinkedIn, for example, would have such a db, since people surf LinkedIn from work. However, they're not granting access to it, I'm sure.

Who else could generate a strong database like this?