That's the thing people aren't likely to share until they've done it. Part of it should be because you have expertise in that field to share but given some of the absolutely rubbish facebook pages that have huge followings I'm not sure that my old school logic applies to kids. Think about what you know, and how you intend to monetise the page and that might answer your question - probably more appropriate than trying to be spoonfed a niche by strangers.
I will surely gonna monetize them in Travelling related issue. Tours and Travel business is now very handy and people would love to travel different tourist spot. You can use your fan page to book hotels, buying air tickets, booking local sight seeing agencies. For me there are thousands of buy and sell platform. Tours and travel looks to me very profitable section.