I'm not sure how much it'll help, but I've started a few suggestion lists to compile the various suggestions that people have made for some of the more difficult squares. I've added other lists here too.
So far there's
Main Street Station 3* (trip across the US / has a national monument on the cover)
Frontierland 4 (travel by boat / title spells 'river')
Main Street 13 (the politician/lawyer/civil war one)
Railroad 14 (New Orleans Square - the suitcase/overseas travel one)
*This one was started by The better to see you, my dear.
If there are other squares you'd like to see lists for, please comment. If you have suggestions for a specific list above, please comment on the list page.
Hope this helps. I'll edit this post if I make more lists.